Hence my idea to remove the negative voting altogether. Will remove the opportunity for voting based on opinion, but will still give you an idea which posts are most interesting.

I like having both. The idea is not just to point out good posts (it's worked very well in today's DrumBeat, BTW, highlighting Darwinian's post about Hirsch). It's also to hide spam and such.

In this case there should be separate negative and positive votes. I may post extremely interesting, but controversal opinion and 10 people may appreciate it and vote "for", 11 people will disagree with me and vote "nah", and my opinion will be labeled as spam, because it will have a negative rating of -1. You can't force people to vote irrespective of their opinion coinciding with the post, or just assume they will.

The net result is that 1000 people coming later on the thread will probably ignore my opinion altogether. On the other hand if I see +10 and -11 on some post I will be interested to read it because I'd see it has provoked some interesting reaction among people.

[Edit] In addition to that, opinion-based negative votes will move my comment downthread, which will make it even harder for people to notice. Maybe sorting upthread should be based only on the positive votes.