I quit the Effective Altruism forum due to a new rule requiring posts and comments be basically put in the public domain without copyright. More info. I had a bunch of draft posts, so I’m posting some of them here with minimal editing.
In a debate, if you’re unfriendly and you make a lot of little mistakes, you should expect the mistakes to (on average) be biased for your side and against their side. In general, making many small, biased mistakes ruins debates dealing with complex or subtle issues. It’s too hard to fix them all, especially considering you’re the guy who made them (if you had the skill to fix them all, you could have used that same skill to avoid making some of them).
In other words, if you dislike someone, being extremely careful, rigorous and accurate with your reasoning provides a defense against bias. Without that defense, you don’t have much of a chance.
If you have a positive attitude and are happy to hear about their perspective, that helps prevent being biased against them. If you have really high intellectual standards and avoid making small mistakes, that helps prevent bias. If you have neither of those things, conversation doesn’t work well.