I think that YouTube algorithms are so smart right now that YouTube doesn't need dislike button anymore it can simply rank bad videos so low that you don't even know they exist.

Edit: YouTube algorithms are so smart* I was exaggerating using hyperbole(figure of speech) in order to imply strong impression and feeling that YouTube algorithms are good enough for YouTube to afford dismissing dislike button.

Instagram is doing fine with likes only so I don't see a reason why YouTube wouldn't. Go to comment section to say what is wrong with the video you are watching or use report button if the video is violating TOS.