You would need to connect men not being as prevalent in child care profession roles to some sort of systemic harm. Or women not being as prevalent in construction worker roles. Just because there's a discrepancy between the two genders doesn't mean there's systemic harm stemming from it.
the harm in child care and education should be obvious: children need role models of both genders. in no other profession is it as important for gender parity to be enforced. so at least in that area there is most certainly a systemic harm if one gender dominates.
every adult the children come in contact with is a role model. children don't select their role models. the amount of time that children spend in kindergarten and school makes that inevitable. for good and for bad. you can't not count on children getting their role models from there, but you can't even avoid it. children need role models from both genders. and if there is no gender parity (or something reasonably close) in education, then they are not getting the role models they need.
I've thought a bit about this since you made the comment, and I think your point about education in particular has a lot of merit. I would normally dispute how you phrased your last sentence, but I've noticed this decline in how boys perform in school, and also noticed that the teaching profession is highly gendered. Thanks for the discussion, you've given me a bunch to think about.
