Sex and hippies, as subjects, naturally seem to go together.
Whether we're discussing nudity in general, uninhibited sex and more, a person can't think of hippies and not eventually turn his/her mind to free love and flower power.
Some background about the hippy subculture might help.
In our history there have been groups of nature worshippers, nudists, hippies, vegetarians, health conscious yoga stretching free love people, and all the cliché exchanges people make about hippies. Some human beings gravitate to the freedom that a hippy commune can provide. It's been happening since we crawled up from nature worshipping past.