I know that happens and I suppose we could look into tightening the screws a bit, but it feels to me like a step too far to exclude those sites from HN.
Some of the opinion sections get extra downweight - that might be helping a little.
>>dang+(OP)
Please don't tighten the screws. They do have great articles, and I really don't think those threads become problematic at a higher rate than others.