IMHO you should be downvoted for comments such as "It's not because anyone in the Republican party actually cares about any of this". This dismisses 100M+ people and their beliefs.
It's why I rarely downvote a comment despite errors or political views (from my stance I much prefer to argue the point giving my reasons). That said, some comments are just so wrong and or egregious that it's obvious additional comments won't help and if posted they'd only inflame things further.
I've learned this from experience, on more than one occasion I've seen HN delete a complete thread (full length of the chain to the top) after I made a very reasonable reply to a very egregious comment posted somewhere near its bottom. The poster then took ofence and still others came to my defense and matters cascaded to the point where it was deleted. If I'd ignored the comment or just downvoted it then it's likely the thread would have remained intact. Trouble was many other intelligent comments were deleted in the process.
From my experience, the point you're making almost always arises from controversial topics or ones that are or can be construed as political. For example, I remember when HN deleted a thread on veganism. Discussion started out civilized but eventually went ary after an extremist made statements that no reasonable person would have considered correct. Backlash followed from multiple posters and HN ended what was no longer a discussion but a heated argument.