Here's my idea. A positive and negative feedback, like we have here, is inherently adversarial, and leads to people chasing upvotes. A better way might be to have one option - you 'reacted' to this idea - good, or bad. If you didn't, you just leave it blank. The most 'reactions' would help show what people are interested in talking about, but without the need for pointless thumbs up.
[Edited because I wrote this quickly]