[xoxoxoBruce]

But how do they know what the speaker will say until they say it? Track record? How do you know they haven't modified, or have more compelling evidence, for their position.
"Examined thoroughly and discarded" by whom, your teacher, your mentor, your friend, some "committee", or you? If it's not you, you're not receptive to outside ideas, and would seem to be a semi-intellectual.
Even if you think they're a one trick pony, you might be surprised you can learn something from them. If you are sure of what they will say, any disagree with them, that's fine, but does that give you the right to deny others the opportunity to hear and make their own judgment? That's McCarthyism.