Yes, I recognize there are some narrow exceptions such as libel, and I'm perfectly fine being held accountable for libel. If I post something which actually libels someone, i.e. something which a court will hold me accountable for having posted, then that's fair, and I'll take full responsibility.
What seems to be in question here, however, is whether people may post truthful comments on twitter, which under U.S. law are by definition not libelous.