I think bikini armor is fine in non-realistic or cartoony settings. Imo a lot of people just have a problem with half-naked women, is all. I mean, no one complains about other impractical tropes, like ridiculously spiky armor or oversized weapons etc. No one wonders why barechested barbarians don't look like pin cushions full of arrows, either. I mean, if you don't wanna look at scantly dressed women for moral reasons, fine, just don't pretend you care about "practicality".
When it's a somewhat serious/realistic setting, though, it's completely unacceptable.