Facebook is getting real crowded (as far as pages are concerned) and a big reason is because there's a lot of advertisements. I don't have anything against advertisements by any means, they allow resources to not cost me money, directly at least. However, when it becomes an eyesore it's a little much.
Also, yes, they are going against the original mission, but missions should evolve over time. Things change from college to when you're out in the world, and as Zuckerberg evolved as a person, so did the mission of Facebook. Most of us would do the same thing if we were Zuckerberg, I know I would have.