Why, do you ask? Because the alien change is a change that morphs the entire property. This isn't fanboy nitpicking; complaining about colors, clothes, voices or the like. This isn't trivial change; this is a monumental change that not only changes the namesake, but changes the characters themselves. This has moved beyond basement dwellers territory, and into the public.
Whether passively or aggressively, people at great numbers are against this change. However, that didn't stop show host Jimmy Kimmel from typecasting all of the people against this change into Internet wackos with no life:
First of all, great job ripping off the Animaniacs:
Secondly, what makes you so much better? The fact that you had a team of writers craft a skit to riff us makes you no better. Yeah, you're on TV. So what? Most people have been on TV multiple times, and have most likely gotten more viewers than you do nightly. Conan was able to get laughs without poking fun at the audience:
Probably shows you why he's got a better time slot. I can see how you'd say I have no life: I did create this blog just to bad mouth Bay's decision and I pointed out the Animatiacs short that you ripped off of. That doesn't mean everyone against this change is like the fat guy at the beginning. Guess what? Most people aren't. They just don't want to see TMNT devolve into crap because of change that didn't need to happen.
Now personally, I'm all for trivial change. If you can make it work, go for it. If the namesake and the characters are still the same overall, I'm in. But a line needs to be drawn in order for it to even still be considered the same property. Otherwise, you're just better off kickstarting your own franchise. And to all you people pulling the "get a life" card: if you're spending precious time complaining about our concerns, take your own advice. Because you're no better.