Can't really add much to what @bashadow said... the "random downvoters" are just some disgruntled people who got extensively flagged for plagiarism, spam and shitposting. The particular downvote I am thinking about (I get it, from time to time) is all but worthless... it's something like a 2% downvote from an account with 50 Steem Power and perpetually 5% remaining voting power. 

It's effect is meant to be purely *psychological,* to make newcomers feel unwelcome and thereby "hurt" Steemit. I have learned to just ignore them...

=^..^=