The part about the show being all about "look how weird these crazy nerds are" is the part that makes it nerd blackface. I'm not against poking fun at groups of people, but there needs to be creativity and substance to it, which I've never seen BBT do. I'll fully admit I haven't seen anywhere near all the episodes of the show, so maybe I missed something there, but based on what I've seen there's pretty much nothing redeeming about it.
If you think Big Bang Theory is liked by critics at anywhere near the same level as Community you're just not paying attention. I'm not saying critical acclaim automatically makes a show good, but Community clearly has way more of it than Big Bang Theory.
CBS is the Activision of the television world. Every company is out for money, but different companies have different standards for how much artistic quality they're willing to sacrifice in order to get that money. CBS, like Activision, doesn't give a **** about quality, and will ride any successful brand into the ground (Call of Duty, Guitar Hero, CSI, NCIS). Call of Duty sets new sales records every year, and CBS is perennially the best-rated network on TV, so some people are obviously okay with that, but I don't like it.