However, interesting conversations are missed because of noise (e.g. down-votes) - I'm less likely to interact with a down-voted post, they usually are not as informative or interesting.
Proposed solution - abolish negative points entirely, points should be per-thread, not per user. If a user is causing frequent problems (frequently downvoted), per admin review then issue ban/rate limits, etc.
I view the positive/negative points mostly as a sentiment rating - if I receive downvotes I can tell my point is unpopular/uncontroversial, if not I know someone found it interesting. That does affect how I post in two ways:
I make more effort to expose common context for posts which are down-voted, people who are lazy and don't care won't read the expanded post, people who are more open-minded (the ones I want to attract and start conversations with) are more likely to come around to my viewpoint, or at least offer more interesting conversation (disagreement is necessary to have a discussion).
So I find both positive and negative votes to be useful, even on my own posts. Even the manner in which I've been down-voted recently tells me something, and it tells me valuable data about who has which opinions.