The problem is where we draw the line. I have to admit I'm even considering the idea of $2 a month as appealing if it removed ALL ads and improved performance. But then we've just enabled a subscription model for a currently free website. It's a downhill slope. More and more premium channels as posters are attracted to the higher returns. More and more crap on the free side of things.
YouTube has no real competition so we'd be trusting Google's "not-quite-evil" attitude towards customers to mediate the process and prevent YouTube from being destroyed from the inside out. I'm not sure it's worth the risk.