I actually prefer the existing 'Like' system. Allowing the ability to 'Dislike' a post makes it very easy for genuinely good content to get trolled right off the front page before it ever gets a fair shot. This way, everything gets a fair chance, and the chaff will fall off as the quality content rises to the top. If you dislike something, that's what the 'Hide' or 'Mute' options are for.