First: doing harm to who? Gimp's an open source software that's been a boon to the community for a long time. I don't even use it, but I welcome its existence - it's not a virus, nor is it a bad influence upon the world since most people not inclined to use Gimp can stick to alternatives.

> But because it exists it means someone who would do it better has less incentive to do so.

That makes no sense. There are a ton of great image editors always striving to do better in the same domain - Affinity, Paint.NET, Photoscape, Canva, etc.