But people do get told that. They downvote anyway.

The problem is that the big Hacker News personality type is one that gets very intent about arguments. I absolutely do. And when you're in an argument, even if you think the response is intelligent and contributes there's a kneejerk desire to downvote and hope that the hive mind will follow you and downvote. I'll admit that I've done the same, on occasion: it's a very pervasive mentality.

It helps not being able to downvote until you have a certain amount of karma: it gives you a period of time during which you need to learn to respond intelligently. But that isn't an entire fix to the problem. Thankfully, to date it's still the uncommon thing to happen.