As far as biological reactions go, in certain countries lots of people visit public saunas naked and find nothing sexual about it. People’s perceptions of nudity vary by culture.
The keyword there is visit, it is consensual. People kiss on the lips without making it sexual as well but you still need consent right? If all parties consent I have no problem with it. Why do people have a need to expose others to their nudity or to sexual content against the consent of other people? Even nude beaches have a sign so that non-consenting parties can stay out. That's my standard for public nudity, it should not be allowed everywhere just in areas line parks and beaches with clear signs for others so long as there are similar public places where people who don't consent can go to.