Another example, Why I do I feel the need to close the bathroom door when I take a dump ? Because it considered taboo or weird. But if more and more people take a dump with the door open, it will be less weird.
Its a hassle too to have to keep things private.
Even if norms change to be far more permissive, there will still be issues with this. Besides, norms are never that permissive in absolute terms since some form of hierarchy quickly sets itself up in response to changing circumstances. For instance in some past contexts a young man might want to hide his promiscuity and adventurous experiences, whereas in some modern contexts he might want to hide his lack of promiscuity and adventurous (instagrammable?) experiences.
To borrow your analogy - even if most people become comfortable with open-door-dumps, why should we force someone who isn't to do it?
Until we stop judging each other, the right to privacy seems pretty important. That doesn't mean you always have to exercise it, but it should be your right.