I learned early that you'd better know what you're talking about. You'd better realize that certain issues are going to be so hot - no matter what reason, what logic you apply to it - you're going to be met with an opposition just because their viewpoint is different, and there's no way they're going to accept your reasoning. Furthermore, they're going to attack you because you will be portrayed as not being credible: "You're an actor. What do you know?"