Sure, that may be technically correct and in practice people downvote for any reason they choose. Nothing can stop them. But if they were used to promote viewpoints and better discussion, the end result would be better communities.

As for the "says who?", for example, that is Reddit's official stance on voting, which I quoted elsewhere in this thread.

You've said it would lead to better discussion. I'm not convinced that's the case. I think flagged and grey comments being filtered out actually helps conversations more often than not. Can we empirically determine which will lead to better communities? Based on my experience than nearly every single community with lax moderation (official moderation and community moderation) turns into a cesspool. There's a reason you're here for conversation after all and not on 4chan.

In my experience flagged comments are typically off topic or abusive. I don't recall ever seeing a flagged comment that was an honest attempt at discussion. As for grayed comments that are an honest attempt at discussion? Very common. I upvote heavily downvoted comments that didn't deserve it almost daily here. I've also been the victim of massive downvoting merely because I present a viewpoint that the hive-mind doesn't like. If you're only interested in a single viewpoint and don't want to see all sides to a topic, then sure, this system is great. I like seeing more viewpoints and perspectives.