Of all pivotal, important things in this game, this is the one that remains unanswered.

Why in the hell did House effectively destroy Vault 21?

By all accounts, Vault 21 was a paradise, and this isn't exactly something you can discount as mere vault dweller nostalgia or propaganda, given that it's an extremely, EXTREMELY rare case where a vault designed as a social experiment rather than one designed to actually save lives produced exceptional results in the form of a thriving vault filled with survivors who not only came out of the vault alive, but were also exceedingly happy with their lifestyle within the vault.

So why in the hell did House fill it with cement? Why in the hell did he insist on the "destruction" (destroyed it's culture and society, but didn't physically destroy it or it's inhabitants) of the vault?

Presumably, the only reason we've ever been given for this, is because House wanted the vault dwellers as part of his regime and under his control, not out of any form of neccesity or danger they presented.

I've said before that to me, the King is House's Achilles' heel, because while I like House, I'd choose the King over House if given a choice. This? This is in a way another Achilles' heel, because this is a working society that had a new idea, a new way of thinking and a new lifestyle, and it was crushed. Why? Presumably it was crushed not even to save House's society or culture, but rather to support it. Their support was by no means neccesary, and yet he forced them on board as though it were. Hell, he took a decent risk in doing so, since he didn't have any guarentee they'd support him instead of just wandering off, and yet he STILL saw fit to destroy their entire society for that mere chance. If such a justification is truly the case, House's actions are tantamount to slavery.

But we've never been given a clear answer as to the why of it, and it's rather hard to believe; if such reasonings were true, then the seemingly logical and pragmatic House suddenly takes on a new light as obsessive, abusive and downright dangerous. So yeah, let's speculate: why in the HELL would someone fill a vault with cement?

You answered your own question, it's VAULT 21. What is a Vault? A bunker with self sustaining systems. Benign by itself, but consider what would happen should a group of militant dissenters, or worse, The Brotherhood managed to get to the Vault, they could remain entrenched for years with no dwindling in power, food and water.

House didn't do it for giggles, he did it to cover his bases. (This isn't speculation, this is actually confirmed information.)

Source:

"He [House] doesn't want it to be able to return to a fully-functional vault because he doesn't want its former residents to attempt to retake it. I.e. he wants to motivate the Vault 21 dwellers to leave the area. If he had simply sealed off areas or electronically locked portions of it, enterprising smarties like ex-vaulters might attempt to work against him and eventually restore it. With the majority of the vault filled with cement, it can only function as a tourist attraction and small-scale residence.”

— J.E. Sawyer on Vault 21

I've mentioned this before, he ruined a facility with presumably light manufacturing and medical facilities to make budget accommodation. Not to mention that he seems to have driven out all trained professionals and, at the very least, civilised folk (in comparison to the cannibalistic raiders and such he had had to train) by utterly alienating them instead of utilising his position as their legitimate Overseer (which he won fair and square by their rules) for soemthing more constructive. Christ Doc Mitchell (presumably one of the few actual doctors out there by legitimate pre-war medical standards) can perform facial reconstructive surgery; what an intelligent guy it might have been more worthwhile in having around House.

I JUST said the actual answer.

And I neither believe it nor re-call you presenting it last time we had this discussion, which suggests to me that it's taken entirely from that Sawyer quote which is - frankly - an absolutely terrible justification. If an outside force managed to seize the Vault then I'd imagine that House has far more pressing concerns than whether they would use it... like the hostile army that just broke onto the Strip past his own defences and the entire NCR army in the Mojave.

If the Vault Dwellers "retook" it then so what? In-fact that's just plain wrong. House didn't take the Vault, he challenged the Overseer to a game of poker, they agreed and he won - that's entirely within the Vault people's belief system which is presumably why they agreed; as long as House didn't threaten their way of life he should have expected little from them in the way of resistance. When the reason (presumably main reason) Sawyer gives for a potential revolt against House's rule is entirely wrong I doubt very much that there were any other significant risks.

It doesn't even make sense from any perspective, so to prevent the Vault-Dwellers from taking over the Vault and sealing it back up again (which would not affect the operation of anything else on the Strip) he decided that squandering any potential it had by turning it into a very cheap hotel was the best option? Talk about side-stepping a pot hole to fall off a bridge.

It doesn't matter what you think, the fact of the matter is JE Sawyer confirmed the answer to this question whether you like it or not.

I'm not contesting that, it just makes House a worse character because of it, as you yourself have not even attempted to convince me otherwise. Guess House must have forgotten he hadn't actual taken anything from them when he decided to fill the place up; House is indeed the savior of humanity.

House is pretty plainly not a 'people person', but if he was a bastard, he'd easily have just said 'whatever' and caved them in. He stripped all the useful stuff out and filled it in. Personally, I see no big deal with what he did. Vault 21 is his property, he has all the right to do what he so pleases with it.

It's not his property, it belongs to the people who were living there at the time. He had no right to do anything with the place. He doesn't "own" New Vegas, he just leads it. There's a big difference.

I am not sure what it technically means to be Overseerer of vault 21, but if it doesn't mean absolute power, I see how House could take issue with the vault. After all, his vision is to rule New Veags as an autocracy, but the vault dwellers settle all controversy with games of change. House doesn't want his rule to depend upon his luck with the dice.

Alternatively, he may not have wanted to deal with the vault at all. Those things always seem to end terriblely. Strip out the machinery, get rid of the debatably useful people (vault dwellers tend not to have lots of caps, and with the exceptions of PCs and the boomers, are terribly adapted to post war life) and close it down. It may not be an assets, but at least it's not a liability.

To be Overseer of Vault 21 means to be autocrat of Vault 21; the people of thr Vault settle things in their own unique way but arent ideological fanatics bent on having all of humanity ruled by fate are they? They'd have been perfectly content to continue exactly as they had before House dug them up.

If you want see the value in having a vault full of civilised, educated and healthy people then that's just you. I've always been told that HOuse is an industrialist with high plans. Turning a pristine facility into a motel on some dubious notion and driving away the doctors, engineers, technicians, teachers and administrators doesn't seem like a particularly smart option when the rest of your staff are reformed tribals of no formal education apart from some 50's slang ( well if you consider a recreation of the mafia reformed).

I guess when people tell me House is a visionary who's going to reignite mankind that vision is a sign factory.

People keep teelin g me he took everything useful out of the vault, if so to be used by who!

Really? I'll criticise any person who tries to paint their home and yell 'STOP! YOU DON'T OWN THAT HOUSE, YOU JUST LEAD IT!'

Mr. House approached Vault 21 and proposed a game of Blackjack to determine who would have ownership Vault 21, they accepted and they lost. So yes, House by all legal rights OWNS Vault 21. To say otherwise is just dumb, that's like saying someone doesnt OWN their computer, they just use it and the computer someone bought is property of the maker.

Mr New Vegas is actually the Zax computer down there and House don't want anyone messing with him so he sealed it shut allowing him to remain a neutral radio DJ to spin tunes and spit news.

You know, off topic, but the fact that Mr. New Vegas is a robot is a robot really annoys me. Maybe if we saw that in-game I would accept it, but it seems so wrong I can't just accept the devs word on it.

I've never heard of that. I just presumed he came in with his Securitrons and basically said "Do as you're told or else."

It's just another example of House's paranoia. Most of Vault 21 didn't want to have anything to do with him therefore they can't be trusted. It's the same reason he destroys the Kings or hits Primm with heavy taxes simply for having dealings with the NCR.