You're making it all about him.
Sex doesn't need to be "important". Depending on the context, your characters could be having sexual relations for any of the following reasons:
1.) Procreation
2.) Recreation
3.) Make-up
4.) Revenge (in some cases, this can be dangerous water to tread, as it enters sexual harassment/rape territory depending on how you do it; on the other end, it could be someone having a one-night stand to get back at their SO).
5.) Anger
6.) Just for plain fun. Because besides all the risks of disease and pregnancy, sex is fun. No one can deny that lol And if anyone does, you're probably doing it wrong xD
You, as a creator, are the writer. You include sex scenes where you want, just make sure they make sense for the storyline and characters and aren't just thrown in there because "adult comic hurhur". That's the only point he's trying to make and you're the one trying to make it a personal problem from his end.
However, whether it's for procreation or simply recreation, NSFW is required. No ifs, ands, or buts about it. I don't care how sacred of an act you consider it, at the end of the day, it's still content that's inappropriate for minors, as well as content you wouldn't want to be caught seeing at work, especially with all the tight and strict sexual harassment laws that are in place these days.
It's not a message telling people not to read it. It's a "watch out, make sure you're in a place where you can read and you're okay with reading it!" nudge in the side. People who call it otherwise are just getting subjectively emotional over it for no reason and taking it as a personal jab to their work and personal views.
This isn't just Tapastic, this is everywhere.
Either way, just a heads up, I'm gonna be keeping a close eye on this discussion over the next few days just because it seems to be getting a little heated again, and we shouldn't be trying to or intentionally hurting someone or jabbing at their views over something as static and trivial as the NSFW filter. At the end of the day, the rules are there because those are the laws in most countries, and there are still kindness rules here that we should be trying our best to mind. Let's just keep it from turning into a circlejerk, okay? 