That’s not why I don’t ship them, personally I just really can’t stand ships based around the “Destined/Fated Lovers” trope and nothing else. That whole dynamic leaves a really bad taste in my mouth and just ends up coming off feeling forced, contrived and of surface-level shallowness rather than any actual substance built through genuine chemistry and interactions. I feel the same way about Shigure/Akito in Fruits Basket (Who follow a similiar trajectory of the trope if you’re familiar with the series) so it’s not like UsaMamo is unique in this regard.
And especially in the 90’s anime I never got the sense that Mamoru was with her for any other reason outside of Destiny for all the reasons Nadia mentioned so that version makes me particular adverse to the ship. (Doesn’t help that it’s the version where he acts most like her dad rather than her lover due to the widened age gap and Usagi’s lowered maturity.)
In fact I would go as far to say that during Classic when they were bickering was when their dynamic was at it’s best and most interesting in the 90’s anime, it all went downhill from there though.
Same, except for me it’s only heterosexual incest that I have a problem with (due to inbreeding) I make exceptions for same-sex incest pairs though so long as they’re relatively close in age and consenting adults.
Unfortunately neither tier bothered to include Lethe/Mneosyne (nor Minako/Ace which I would’ve also liked to see as far as manga exclusive ships go) but if they had they would definitely be somewhere between “AWOOGA” and “Not my Fave, but fun to think about from time to time.”