"there (sic) chosen sexuality"
First, let's stop this thinking because straight people are the biggest (in numbers) offenders of this. While it is true that kids are more likely to "experiment" with their sexuality, their ultimate "choice" is not a choice at all.
Second, should minors be allowed to show sexual affection publicly? Do adults behave this way? If they do, what are the accepted consequences? I would venture to say adults transgress in this way rather rarely. Why would there be a double standard here for minors?
Yes. School districts do have the right to dictate behavior ----just as the workplace regulates adults. I would not propose a "zero tolerance" policy because they don't work but I would propose a reasonable one. If straight boys and girls can hold hands (which is rather innocuous), why not their counterparts? But as adults, we should recognize, define and resolve issues of harrasment and bullying instead of getting weird about such issues.