You might not believe it, but you actually help out the YouTuber by interacting with their content even via a dislike. The more "harmful" thing is to simply leave the video without engaging with it. It might not make sense to you, but blame the YouTube algorithm which does its best to hurt channels on a daily basis. There is no penalty for a ton of dislikes or a bad like:dislike ratio on videos. If you want proof of that, just check out the CoD Infinite Warfare or Ghostbusters 2 trailers.