I'm more old fashioned when it comes to things like this. I tend to think just because one isn't ashamed by some part of their body doesn't mean it's appropriate to leave it unclothed in public. It's like wearing shoes and shirt into businesses, it is just the appropriate thing to do. Different places and different situations should have different degrees of formality. A church generally one dresses nicer to go into, or remove your hat at the door. A fancy restaurant one generally dresses nicer and doesn't come in in grungy shorts and a T-shirt. A public place for shopping and so on, I feel someone should at least keep top and bottom mostly covered. That includes the 'butt cracks' of course . I don't think it's a matter of being ashamed or not, I just think it's taking into consideration the time and place you are at and the etiquette for that situation.