Well that's exactly why they should. They certainly don't have to answer to me or anyone else for that matter, but it's here where you can express the decisions regarding your own productions and your career. If you put stuff out there, expect to get some criticism - it's just the way it is.
There's also producers here, so what? Me, personally, I rather admit I've hit a wall or that I'm just not good enough for what I aspire to be, and don't try to pollute the scene if I don't think I'm contributing. Is it hard, producing? Creatively, yeah. But why put out half-baked ideas, or accept standards?
As to why do we bother - we all love music and want it to have meaning, not be a production line. It should be art, not entertainment. Why waste time on negativity, I ask myself sometimes as well. Clear negativity could be tuned down, I agree. But I think it's going towards that direction, it was worse before.
Plus, those fans who write "amazing", "toty" etc. usually will forget about the thing in three weeks, once there's something new out. As a producer, would you rather have a thousand people who think you're ok, or 10 who absolutely love your body of work? (hint: depends on your goals)