People are fine reading stuff they disagree with, it’s fun that way. They just downvote if they disagree. It’s not fun sitting around in a moderated hugbox where everyone is saying the same thing
Run something unmoderated long enough and, depending where you are, you'll have law enforcement knocking on your door.
Hacker News has downvotes and people here disagree all the time. It's subjective but it even feels like downvoting and disagreement have increased over time, so the presence of downvotes at best doesn't seem to have an effect and at worse seems to encourage disagreement.
In fact, I actually can't think of a platform for which your claim is actually true.