I don't think it's odd, tbh. People downvote stuff they do not agree with, even though the downvoted statement contains no opinion nor attack. That's just how people behave online.
Normally, there is no issue with people downvoting stuff on the Internet. But on HN, voting results in karma, which results in rights. Downvoting is therefore taking away rights, and as seen, on the basis of just opinions. Since downvoting itself is a right, opinions on HN are shaped by those that hold power with this right over others. HN is, more than any other place, enforcing its own filter bubble.
Not sure if people care about this point on HN. I mean if downvoting someone cost 10 of your own karma, then you bet people would use it more judiciously.