I think cups are a little different since men don't wear them all the time or wear them to be less alluring.

And that's the main problem I have: they shouldn't be different. Whether or not a man wears a cup is his own business. Likewise, whether or not a woman wears a bra is her own business. I am troubled by the assumption that a woman's dress is anyone's business but her own.

If a man around me believed I was being "alluring" by not wearing a bra in my own home, I would let him know his assumption was the issue, not my choice of clothing. I can guarantee that would be his attitude, if I commented on his junk flapping freely in his pants instead of being contained by a cup. :-)