If it's any consolation, most people treat the 18+ tag as a general content warning. They're saying a game [i]might[/i] devolve into smut (or splatterpunk, or dark themes or w/e) if one thing leads to another, not that it definitively [i]will[/i]. Essentially it can mean "I'm not going to censor myself or my content, so be aware of the possibility of smutty themes if our characters have chemistry."

I don't like writing smut but I've never felt uncomfortable signing up for games tagged 18+.