|laziness, impatience, and hubris|
If multiple people who used to be reluctant to downvote at all are becoming quick with the trigger, maybe that shows the extent of the problem.
That reason reeks of intolerance. It was used to suppress entire populations.
The other argument is that you need to block these posts from new users. However, downvotes do not help at all for that. Firstly, because they cannot see the rep of a post (unless they voted and already have their own opinion about it.) Secondly, points do nothing. Indeed, downvotes seem to just release pressure for those who vote. Like honking your horn after some idiot cuts you off.
If PM wants to quash a certain user, than quash him. Have a vote or something and just do it. Downvotes achieve nothing.
In reply to Re^6: And here's why I think "downvotes" should be eliminated, or tabulated separately ...