I think there are way more good actors than malicious ones. And the reputation system along with the power of the community is great for dealing with bad actors.

As for paying to vote: You can kind of already do that on steem. It just requires hunreds of dollars of investment to have even a $0.01 vote. And that's still pretty much nothing compared to the $300 votes of whale bots that make or break posts.

But yeah, it most definitely is tricky stuff :)