You need down votes to keep the spammers and scammers at bay. They're also useful for pushing down posts that are poorly written, "first post!" comments, posts that consist of the sole word "agreed," and the like.

Unfortunately, there's no way to prevent people from downvoting because they disagree with the poster. Since this is mostly an anarchist site, at least at the moment, a thoughtful well written post about, say, Jill Stien, is going to get downvoted into oblivion because of the opinions expressed. That will remove the opportunity to open a discussion (pointing out the multitude of reasons Jill is a horrible choice), and risks turning the place into a echo chamber, where we only hear what we agree with.

One solution would be to give less weight to a down vote than to an up vote. Instead of a single whale downvote canceling out a hundred guppy upvotes, make a downvote only count for, say, 1/4 of what an upvote is worth. That way the truly crappy posts and comments could still be squashed down by the masses, without having to worry about ticking off a single whale and losing everything you would have otherwise earned.