I chose the the minutmen plotline, is not Brotherhood of Steel, far of what Minutmen strive for?

I got that feeling with the Covenant faction as well, not that I decided to go down and kill them all just to get their colony, but they where like a brainwashed cult, and BoS no offence matter how cool they look in their armor. They are a bit extreme. And to go from being a General to bu sub to Pal.Danse, dont sound like a great idea, his way of suttle is to charge in everywere, and thats a problem with no permadeath, Since the mission I did with him I had to save his [censored] about 4 times.

But back to the question.

Can I join several factions with out any backlash?

Until certain point of the main plot yes, you can join all factions, including the Institute. The game will tell when you need to decide for one faction over the others. So, if you want to do most faction quests, dont advance the plot too much.

Being forced to choose was something I loved and hated at the same time, on the one hand I wanted to play it down the middle but on the other being realistic its understandable that supporting one faction will put you into conflict with another.

To answer the OP :

I always took the BOS to be very insular and inward looking, not wishing to help others but simply act as a bunch of power armoured magpies. Fallout 3 made quite a big thing out out of this with the Outcasts having left the original Capital Wasteland BOS as they felt they had deviated from that. Then in F:NV the BOS basically live underground and never go out.

I'll do the BOS questline at some point, but I'm definately a Minuteman.

Well BOS in Fo4 dont seem much better. Pal.Danse is probably funy to have with you, but man his survaving squad brags about how good squadleader he is. Well he got all other members killed, because he prabably charge in both on Raiders and Mutans;)

I probably have to side with him for getting th Powerarmor, not that I use them Have three already nicely painted, stored at each camp.

But its nags me a little that I cant just be allied/ friendly but have to join. Since joining and the quitting would seem as a betrayal of an oath.

Any of you lot heard of spoiler tags? Just saying.

Yes, I posted no spoilers.

The Minutemen and the BoS are actually very different.

The BoS is focused on the salvation of mankind, and believes that the best way to ensure this is to collect advanced technology and hoard it away from anyone who might misuse it (so anyone who isn't the BoS).

An example: a BoS patrol comes across a settlement being attacked by raiders. There are no Super Mutants, Synths, or advanced technology involved. Just a bunch of people firing pistols, rifles, and shotguns at each other. The patrol doesn't intervene, as there's nothing of interest to them. They would step in if Mutants or Synths were attaking, but if the settlers were using Energy Weapons of some sort while the Raiders were using Guns, they'd attack the settlers instead. The important thing is putting down abominations and collecting advanced technology. The fate of any given person or settlement doesn't matter. All that matters is the preservation and salvation of humanity as a whole.

The Minutemen, on the other hand, are all about the people. In the above example, they would swoop in on the side of the settlers, regardless of who was attacking or what weapons were being used. In addition, the Minutemen tend to use Laser Muskets, which the BoS wouldn't allow.

Incorrect, as one of the radiant quest givers specifically says that they're keeping the "trash" out of the Commonwealth, and sends to on what amounts to "blow up this raider base/Super Mutant base/Ghoul den" missions. You aren't there to pick over tech, just wipe out everything that's home. They'd aid in the defense of the settlement because it's part of their mission.

At least Maxon's BoS. The western BoS does exactly what you said.

You might want to reread my post. I mentioned that they put down abominations as well as gathering advanced tech. I don't say so in the last sentence, true, but I do mention it.

Also, it's worth noting that the FO3 BoS had a split because Lyons decided to help people. The Outcasts, who followed the original charter of the BoS, disagreed with this. It's also stated in-game that Maxon returned the BoS to the original tenets when he took over.

So why do you loose settlememts to the BoS if you arrange them to give food, weather purchased or donated? Remeber the words of Elder McNamara, "We do not help [outsiders], or let them in." Maxon is already letting Wastelanders join up under a sponsorship program that operates much differently than the prior "rare exception" rule. And loosing settlements means that the BoS have taken over said settlements, which is helping to protect them from raiders and the like. They don't need to after they got the food shipment, but they stick around anyway.

Maxon hasn't fully gone back to the old ways, but he's not in Lyons' camp either. He wouldn't have supported PP at all until it was completed. He's after tech, but it doesn't look like he's harrassing people over every little blinking gizmo unless said gizmo can actually destablize the region. Laser gun and PA owned by a waster? A bit excessive, but fine so long as they aren't creating problems. A waster in control of the rangefinder to an operational Kill-Sat? That's something they need to take care of immediately.

Maxson is more or less a genocidal maniac, out to exterminate ghouls as well as synthsas well as anyone who disagrees with him, not to mention the usual targets of Super mutants and Ferals.
Same sort of nutty fanatic as Father Elijah was, only more charismatic.

Battlestar explored the matter of biologic synths too.

If they can breed with man, they are human, by all standards of modern biology.