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.

I believe this is also true for Hacker News.

First downvote can be used for arguments like "let's increase taxes to the rich because, this way we can build more fair society, European countries have shown that high taxes..."

Second downvote can be used for comments like "Let's tax these rich bastards".

I want to also mention reddit voting system which I kinda like: they have downvoting, but they also have a sorting by "controvervial": top comments are the comments with high number of both upvotes and downvotes, such comments really help to see the full spectre of opinions in discussions, while the universally true and not interesting comments everyone agrees with like "we should not kill people", are below controversial comments.

Having it work that way would significantly discourage using upvotes and downvotes as agree/disagree buttons, and make it much clearer what the community thinks of any particular post or piece of content.