The fact that you put it in a public forum makes it very likely that someone who does like them will read it, though, and then what? Then you've made someone angry or hurt for no reason other than you couldn't contain your negativity. Freedom of speech pertains to political freedom, not the freedom to be an ass just because you want to be.
And before you get it in your head that I'm defending the band because I'm a fan, I'm not -- I don't even know their names, and my musical tastes run more hipster than radio pop. I just find unnecessary negativity to be tiresome.