Fallacy: appeal to free speech
Person 1: It's really reprehensible that X says this or that.
Person 2: X has a right to his own opinions.
The problem is that this is a non-sequitur. The person in question did not dispute that X has a right to free speech, he only disapproved of it - which is his free speech right (much to the chagrin of Sarah Palin and others who believe the First Amendment is meant to protect them against criticism). Stating the obvious does not add anything to the debate. So don't.
Conservatives have a habit of doing this when the behavior of the religious lunatics who are in league with them is criticized. It is a neat way to divert attention from the substance of the matter, namely, that they are using their free speech rights to do something that is not respectable. Instead of debating the substance of the matter, the interlocutor of the conservative will be forced to affirm the obvious, and waste valuable time in the process. In the meantime, the substance is completely forgotten, and the conservative's objective is achieved: their loony allies have once again escaped from legitimate and reasonable criticism.