It's like saying "I just bought a car and I"m happy with it but I still like to look at other cars at the car show or in the showroom because it makes me feel good".
Seriously; unsolicited negative comments on pretty much any aspect are not ok. Sexually charged comments are not ok in most environments. But I don't want to live in a world where complimenting someone on their appearance is a bad thing.
Add: Agree. I'm truly baffled by the parent comment.
People say things about appearance all the time. And I can't think of many cases where a comment (positive) about how someone appears (if said in the proper tone of voice [1]) is not appropriate. And even in the case of a negative comment you'd have to take the relationship of the parties into account (agreeing that that's a much broader situation and safer to not say anything).
[1] Of course I can think of many other exceptions (person dying in the hospital and you say "you look great") but the parent comment doesn't appear to be suggesting fringe cases.
What are they? I'm curious about what is prompting downvotes other than the obvious sorta somewhat non-pc patina.