But the parent wasn't doing that. He was just taking the opportunity to dunk on his outgroup, by insinuating that people who are opposed to universal healthcare are selfish people who would rather hurt themselves than help others (which you will see is patently untrue if you actually get to know those people, but I digress).

If the parent had instead chosen to give a thoughtful response focusing more on a positive message (say, exploring how we should do more to help others and how universal healthcare can be a facet of that), that would've been fine. But yet another post of "my outgroup is evil" doesn't teach us anything or lead to good discussion.