i.e. allowable, if mutually desired, between lovers within relationship to each other, but not to be traded/sold/distributed. That would respect the sexual privacy of relationships whilst providing a safeguard against an abuse potential.

You later claim that viewing (an isolated personal act) is inconsequential. This appears to be a well grounded view, so why do you claim that a relationship (an immaterial construct) deserves privacy, and that this should be enforcable by law, whetever the subjective persons involved say?