Most of the things we think of as harms also interfere one's heartbeat, with one's brainwaves, with one's breathing, with one's digestive systems, with one's sleep patterns, etc, since we're our biologies and every biological function is interconnected with the other.

Indeed, and for this reason, we might be able to measure harms indirectly by looking at heartbeat. A doctor actually does this sort of thing - he looks at your vital signs to see how you're doing.

Nothing I wrote should be interpreted as excluding these other ways of measuring harms. I was talking about one measure, but that doesn't mean there aren't others.

your whole argument [could be read as] trivially true...

Indeed, and I expected it to be read as trivially true, and therefore as the claim I was responding to as trivially false. I wasn't expecting any pushback on such an obvious point. If drug addicts really are harmed by drugs, we should expect this to show up in lower reproduction. It's really quite a trivial point.

I also don't expect they do well in the life expectancy or health or prosperity department, which is a more customary method of determining well-being and "harm" than "number of descendants" is.

Indeed, but these other respects aren't relevant to the claim I was addressing, which concerned the reproduction of drug addicts.