There are some huge spoilers here, so I'm censoring most of my post

They need to kill off the leaders to make way for your ascension so that is unavoidable.

I guess it is fitting that the Brotherhood be the one guild which gets nearly wiped out everytime.

But why, if you join, its like asking to get killed. I mean, the other guilds only had a couple of casualties, instead, the DB nearly gets wiped out

Well to be fair that sort of goes with the territory, as an assassin you will eventually be pissing off a lot of people. Honestly I see no reason to join them. I do admit to really enjoying raising their sanctuary to the ground, best decision for the DB that Bethesda added after Oblivion. The DB annoyed me in Morrowind, annoyed me in Oblivion, and between their horrifically pathetic attempts to kill me and their general existence, they annoy me in Skyrim.

That being said I can see why those who want to RP an evil or cut throat style of character would join them, feels appropriate.

And you know this how? Only because you've played before.
The DB is a secretive organization that most people only half believe in as a scary story. Even the kid you get the first quest from was surprised when his ritual actually worked and you showed up. There is no way a new prisoner entering skyrim would know what happens to assasins in TES games.

Well, I see your point, but I'm talking about ordinary people, I mean, the Dovahkiin can do whatever the hell he wants with few repercussions, just because he is that powerful, so he is kind of the exception to the rule.

Yeah I would have destroyed the Dark Brotherhood on my first playthrough if I knew it was possible, sadly, I did not. So I had to do it on my second.

Simple answer....money.

Depends on your perspective. What if I didn't want to
Then being part of another organization could be the worst.

Because in real life, you can't see into the future.

if you like to kill, and like lots of money, then the dark brotherhood would be a perfect choice, plus theres something appealing about joining a secret organization, witch has guidence from a higher power, personaly the dark brotherhood are my favorite guild.

just desserts and overall i felt that the db questline was by far the best in the game. so much emotion, colour, and bloodshed.

In real life no assassin organization can survive because it doesn't need a rocket scientist to link murders and find out who did it. Also, murdering psychopaths usually have a hard time getting along with people.

It's a profession. Some people need certain people taken out, and you are there to provide a service. Not much different to hired swords really.

luckily, it's a game

The problem is that DB's hit list knows no bounds. Hired swords can decide whether they take a contract or not - the DB is just a passive instrument of indiscriminate barbarism. The game just has us kill random, perhaps evil people but there is nothing to stop the DB from hitting people like Jarls, priests, random traders trying to make a living just because someone gave you five hundred bucks to kill them for whatever reason.

DB is a good idea until you are the guy who is being hunted because you unknowingly stole someone's girlfriend, or were rude to someone because you've had a bad day.

Yeah, because when you join the leader comes to you and tells you "Just to let you know, after a certain number of contracts you'll have to kill us all because one of us will rat us out ".