Well as far as the YouTube algorithm goes, dislikes *are* positive growth, and are essentially for all intents and purposes no different from likes. The only thing bad about dislikes really is that other people can see them and perhaps make judgements on the quality of your content based on them - along with however you might feel about them personally. As far as the algorithm sees it, it's just another interaction (like likes, comments, etc) and actually helps your SEO.
YouTube follows the age old media principle of "if it's controversial, it'll do well" - that can be good controversial, or bad controversial. You can have a video that's purely like 30,000 dislikes and YouTube will treat it the same as if it had 30,000 likes, because it's still 30,000 people who felt compelled enough to interact with the video and stay on the site a little longer.