No, defend it. That's what's called for when what you're expressing an "honest opinion" on is a matter of fact.

I mean, if you were to say, "I think Saddam Hussein was a sexy stud," that would be an opinion requiring no defense (no matter how many people might disagree), because it's purely opinion, in which your feelings are as good as anyone's. But when you say something that is potentially provable/disprovable, and you're challenged on it, then the burden of proof is on you to provide evidence in support.