While I agree Robertson is a wack job, the First Amendment does indeed protect his right to say what he said. No matter what the Venezuelan govt. wants the Bush adminstration to do and no matter how much they want to believe he is a terrorist, he has done nothing wrong except be a class A moron aloud with media around!
This continues the common problem of raising the First Amendment. Critics tend to not question somebody's legal right to say something (a genuine First Amendment issue). They tend to criticize by saying that they 'shouldn't' say something: that is, criticizing the substance of what the other person said, or otherwise criticizing their judgment.
When someone says something dumb, inflammatory, or worse, their legal right to say it is not in question. Raising the legal right to say something in response to a criticism of words or judgment is silly.