But sometimes the comment doesn't actually give feedback. If someone says "This is dumb" that's no more helpful than a downvote. In fact that could cause potential arguments than if you had just let it be. I've seen plenty of people respond to feedback with abuse that they didn't know that they were talking about.
That said, there's a lot of threads that get posted that are dumb. The example I've given before is "MAKE X SKIN FOR X CHAMP" and the description is "PLS DO IT RITO I WILL GIVE YOU ALL MY MONEY!1" why do I need to comment on that to downvote it? (I can literally see 3 threads like this on the forums recently by the way) Clearly the poster hasn't put time an effort into it, so why should I be forced to say 'that sounds bad' to downvote it? See the issue? There's a lot of spam on these forums or people who spam the forums, and people up/downvoting it are their way of regulating it. Sure, a lot of stuff gets downvoted, but stuff does come through. For example this guy from yesterday. I had a lot of spare time yesterday (ah render times) and that was honestly the post that had the most effort put in, and it showed. That's not to say I spent the day sitting there downvoting everything, but I can look at a lot of them and think 'yeh that sounds stupid'
Now even more relevant is this thread. I disagree with it. There's been a big attitude recently on here about downvotes being an issue with petitions to get it removed and what not. It's little a little pixelated up and down arrow. I've no idea why people get so worried about it. So what if your idea didn't succeed on the internet.