I personally love and embrace the Dark Brotherhood. Yes! I said it, I love the Dark Brotherhood as much as the Volkihar Vampire Clan.
I personally find them to be better company than the Thalmor, but here's how I see it.
There's a lot of stupid NPC's out there in Skyrim that deserve to be picked off. Some people in Skyrim are better off dead in Nirn and I feel that any NPC that dies by my character's hand is an honor as well as a privilege to be had.
I mean every person that I've killed has been really mouthy and disrespectful and Grelod definitely deserved an arrow between the eyes the way she was cruel to the orphans.
However I think being the Dark Brotherhood is a point of view. I think they do Tamriel a good service by getting rid of a few bad people. I know some good people get hit in the cross fire, but I think the fact that they strike fear in the hearts of man and mer keeps some people in line. But thats just me.