You said it "I need to root my phone and thus void my warranty". If you void your warranty you are free to do whatever you like with your phone. If it was "truly open", you wouldn't have a warranty.

It's always a balance - do you want something you have complete control over, including the possibility to break it, or you want limited control but be sure that even if it breaks, you get a new one? The platform itself is "open enough", but manufacturers and carriers are making a business out of it.

And for the record, I think you can click "clear data", and also use some process monitor to kill your unwanted apps. My facebook app doesn't have these issues