I'm religious, but speaking within the materialist framework I'd say that the uncovering of oneself is part of a mating ritual, and that by giving such a signal

I'm religious, but speaking within the materialist framework I'd say that the uncovering of oneself is part of a mating ritual, and that by giving such a signal one without the need one is in some way being dishonest, abusive (i.e: to harass or take advantage of) or even enroaching on the relationship of another. If a person were to be exposed in front of a child it would point towards that person having certain desires for that child. As for why uncovering oneself is a reasonable mating ritual, I believe it is similar to how in the same way that if you have a gun and are going to shoot someone you would indicate as such to ward them off by pulling your gun out of its holster.