It doesn't have quite the same effect. There is a lot of content that is neutral but not necessarily harmful. But when someone is posting thousands of comments per day and voting each with dozens or hundreds of accounts in order to try to earn $0.02 each, that is causing a lot of long term damage (all of those comments and votes end up being stored on blockchain forever).
@indigoocean also made a good point about there not always being agreement on what is worth upvoting, and people who don't agree with the upvote policies might then decide not to support the initiative at all. There should be very little disagreement on downvoting aggressive spam and other clear forms of abuse.