In a few European countries for instance, including Germany.

Though, taking Germany as an example, you might run into legal troubles if you make a nuisance of yourselves knowingly or on purpose. [1]

Americans are considered pretty prude, uptight, and christian fundamentalist when it comes sexuality here, while US citizens can have quite the culture shock and think us crazy. The laws surrounding sexuality are really just the tip of the iceberg.

[1]: https://www.gesetze-im-internet.de/stgb/__183a.html

I don't really want random people fucking in the streets, that's not even about the taboo aspect of it. Get a room.

That's exactly the taboo aspect of it.

Replace word “fucking” with any other activity and you’ll see how taboo it is. Hint, try “laughing”, “hugging”, “playing”

A softer facet is kissing in public, or PDA's how they're called by some. I find it ridiculous some people are offended by this, but maybe I am extremely shameless.