One of the most insulting and provoking things you can do during an activist debate is assume that anyone disagreeing with you must simply be ignorant. This is exactly how religious proselytizers think: “Oh, you’re not a [religion]? Let me tell you about my faith, and you will believe.”
In the case of Christianity, I’m not a Christian because I know the Bible far better than any evangelical I’ve ever encountered. In fact, I like to kind of set them up, knowing they will assume I’m uninformed, and then embarrass the snot out of them with how much better I know the Bible. It’s gotten to be great fun since smartphones, because someone can always look that verse up on the spot to confirm that I’m right and they are the ignorant ones.
And this is usually the case with people who assume that it’s impossible for two informed adults to reach two different conclusions. When you meet an opinion with a base-level explanation for five year olds about a topic the person you’re talking to would have had a self-interest in knowing about since, say, 2003, you are clearly the one who is not using your brain.
This feels short, but honestly, what more can one say? Sometimes people disagree with you not because they are fools, but because they have a different perspective. And sometimes it turns out they disagree with you because they are better informed than you are. So be very cautious about “sighing” and “explaining this as simply as possible” and starting in on Wikipedia-style introductions to the topic that’s already up for debate when you have no actual clue that the person is missing some crucial knowledge on the topic. It derails, and it pisses people off, and activists have enough distractions and things to be pissed off about.