As an example, I am well aware of how strict r/worldnews is moderated on IvP topics, so I am extra careful to be factual rather than simply making comments based on more general thoughts, like I do for other areas.
I have responded to some comments in the past by responding by quoting legal cases, news links I sourced my comment from, or from subject experts.
It doesn't matter how accurate or factually proven the comment is. If it's even slightly critical, it'll end up with votes of anywhere from -10 to -50 from all the down votes.
For other people's comments, anything negative that hasn't been down voted into oblivion will always have the "cross" icon next to them, meaning it's listed as "controversial", which is when it has a large number of down votes, plus up votes to balance it out.