Regulation of public sex
America doesn't ban speech based on how offensive it is, and I think this is the best approach. There are some exceptions to free speech of course, things like libel and shouting "fire" in a crowded theater, but the justifications for those are not simply that the speech is offensive.
If we don't ban speech because it's offensive, Amber at Prettier Than Napoleon argues, then we also ought not to ban sex in public because it's offensive.
Other people are unwilling spectators to our offensive expression and conduct all the time. I can stand on the steps of the Supreme Court and wave gory, graphic photos of dismembered fetuses at passing schoolchildren. I can wear a jacket that says “Fuck the draft” in a courthouse. I can put cartoons of Mohammed on t-shirts and wear them on the street. Lots of people would find these things offensive, but we don’t allow their religious fervor, patriotic sentiment, or just plain weak stomachs to be grounds for censoring the public sphere. Why is sex special? To use legalistic language: unlike decibel limits, this is not a content-neutral restriction. (Or is it? Is a dimension of expression, not content of expression? Can I really express myself sexually if I am not permitted to act on my feelings? In the same way that no other words really convey the sentiment "Fuck the draft," does any other mode of expression really get across what a physical gesture like a kiss does?)I find her argument convincing. She has a follow-up here.
Even if you don't buy the sex-as-expression argument, even though it's clearly communicating something between the parties engaged in it, why is preventing offense a legitimate state interest in this case and not in other cases? If you have a right to have sex in your home, we can't regulate it, even if your community knows what you're doing and finds it totally offensive. Why does the public actually seeing it, as opposed to knowing about it, make a difference?
It just seems odd to say that we can burn flags in public (something many people find so offensive that it provokes violence) but we can’t have sex in the bushes at the park because someone might get the vapors.