Reason why it works in that tribe is because EVERYONE is doing it. It's essentially conformity - everyone is doing it, no shame in it thus it is normal and society is fine.

Though the argument in question is sort of weird; you're comparing two extremes (fully clothed aka hijab and nek-ed) and saying if one exists the other shouldn't (effectively). Perhaps a better argument would be well if society can work fine without clothing why should we wear clothes (as opposed to why wear the hijab, which is the exact polar opposite of bein nek-ed)