I don't see what the problem is. Maybe they should be clearly marked for those who don't want o go, but I don't see way it should be a problem for them to exist. As long as they aren't harming anyone (they aren't any more than a clothed beach) then they should be allowed.
Nude beaches are generally clearly marked and do not hurt anyone because they exist. If you don't want to see nude people on a beach, you can go to virtually any other beach. There is no evidence that nude beaches have a higher rate of crime or sexual assault than a normal beach either.
In a free society, we must allow people to do as they please unless their behavior deprives others of their rights or poses a safety hazard. That said, nude beaches should be allowed as long as the nudity is confined to designated areas and warning signs are posted. This way, the interests of nudists and those that would prefer to never see nudists will be balanced.