That's an uncharitable reading of HNs guidelines. I would interpret the following part of it differently:

> Don't feed egregious comments by replying; flag them instead. If you flag, please don't also comment that you did.

My interpretation is more: HN considers polite racists to be a moderation problem, not a hook for angry shouting at each other.

"be the better person" applies. If they are making a well founded statement but you don't agree with it on a moral level, you CAN try and argue with them, but if you get angry at them you lose the argument by default. You can bring up counter-arguments and sources and the like. You can (and probably should) choose to not engage, and just downvote or flag (if you feel like it violates guidelines).

One problem of the internet as a whole (and I am guilty of it too) is that people feel like they HAVE to engage, even if it's futile.

Indeed just as with wiki-lawyers, and everything else with humans involved, the rules/politeness will be used as a weapon by some and all of us who abide are beaten by them.