Earlier quoted context omitted.
It's a question I've been struggling with lately. Downvotes reinforce groupthink, that much is subjectively clear. I've considered solutions, and I believe forcing people to reply before they are allowed to downvote would help. However, in opposition to my own idea, I consider that simply requiring a more effort wouldn't necessarily change the groupthink problem, but would just stifle low effort downvotes. Let's cons…
We could remove downvotes. They had three purposes: 1) Crowdsourced moderation. Well, everyone is using manual moderation anyway. 2) Silencing others. This is a misfeature. 3) Finding the best content. Upvotes are enough for that. That said, I'm not sure this will reduce groupthink. Twitter has no downvotes and plenty of groupthink.
The problem is in my opinion that once people begin to act like this, their victims behave like this also. If you get punished for arguing against somebody, you learn to stop arguing and just downvote that person instead. It's a chain reaction.