>Downvotes are a perfect way to ensure you end up with a hugbox where people are afraid to disagree.

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.