Stay respectful and stay calm—always!
When people are wrong, help them see the most helpful things to help them on their way. Stick to what's useful. When someone says something that isn't useful, saying so isn't useful. Don't fully change the topic, just shift it over a little to some useful idea. Focus on whatever goodness you want more of, not the bad you want to eradicate.
Conflict and disagreement make fragile circumstances. Handle with care. Don't toss eggs on the table. Don't gently roll them away either. Where an egg rolls to it can roll from, then smash.