If America Was A Startup We’d All Quit
techcrunch.com
techcrunch.com
See: http://en.wikipedia.org/wiki/Penny_Arcade_(webcomic)#John_Ga...
Probably the most principled reason to leave would be over US national security/global operations. If I were an absolute pacifist (which I definitely am not), I'd have a hard time remaining in the US, although it would be a case of whether it's more moral to stay and try to change the system vs. go somewhere else with less military spending or involvement.
Taxes, business environment, education, etc. are all issues, but the US has advantages and disadvantages vs. most other countries, so there's no clear choice. Leaving for a few years is quite reasonable, but renouncing citizenship, probably not.
It would be different if the US were self-contained and didn't essentially control the security and regulatory situation globally. Leaving the US actually increases your chances of being spied on by the US or attacked with a drone.