That’s nice and all, but it’s really not anybody else’s problem.

Sounds like fat shaming rationale. If I was 20 and weighed 160, i might be able to sit with my knees squeezed together (with physical effort) without discomfort. However I’m past sixty and considerably heavier. You appear to be asserting that men don’t sit with their legs together because they CHOOSE to man-spread, and I’m sure your most blatant examples certainly do, but asking me to hold my legs together is a like asking you to hold your feet an inch off the floor for the entire trip. You might be able to do it, but only through physical exertion and concentration. Thankfully I haven’t had to ride public transportation for several decades, and I find this discussion on man-spreading mildly amusing.