There are a lot of reasons someone would ban nudity on their land that have nothing to do with complaints or morals. If a sim owner feels nudity is not appropriate to their venue, which it isn't in a lot of places, it is their right to make rules against it. They are not required to accommodate exhibitionists just because they have land on an M sim or even an A sim.
If you want to go around naked that is your business, until you go to someone else's land , then it is their business to decide if it is appropriate. If the major of people that go there don't want to see nudity, then they are fools not to ban it and anyone that insists on coming there nude. It is good business and has nothing to do with morals. If you don't like the rules someone has established, just don't go there. There are plenty of places in SL that allow nudity. Your insistence that you should be allowed to go nude anyplace you want to is imposing your own morals on others too and you are as guilty as the people you complain about.
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Qie Niangao wrote:Or could there be avatar shapes so perfectly matched to their mesh attachments that they don't even need the alphas?
Its often good to wear an alpha anyway if the item covers a joint - some animations in SL "break your bones" when they twist you, and that can create pop-through even on a perfect fit.
With mesh bikinis, there is often so little covered that the outfit never crosses a joint ( 
), so this can be easier to fit into than a full dress suit - I wish I had that problem in RL. 
