Because it's censorship, and I've already seen 3 idiots downvoting out of pure persecution simply for disagreeing with the author, not the content.

I believe that spam is really disruptive and makes any environment dirty, but any content that someone downzaps should be filtered, and the moderators should make the final decision. I've met about 3 jerks here who downzapped out of pure harassment.

To me, Downzaps is censorship; it's people who have no arguments and simply use Downzaps to censor content.