They have a flagging system, but it is a bit abused in my opinion. I think a down-vote button would be a much better option as you said, but we shall see what the witnesses decide to do going forward.
The main reason why I hate bots so much, is because the bots and the people who belong to them don't even read the content they are up-voting, which in my opinion is totally unacceptable.
So they don't read the posts, what exactly are they upvoting? Is it traffic? Is it "copy and paste" blogs?
No, they just up-vote whoever delegates power to them, so basically, the bot gets paid, and the people buy votes. Then the bots find the best content to curate, and just up-votes it without even reading it either.
Hence the reason why so many posts have tons of up-votes with very little comments in comparison.