Porn is fantasy.
Mainstream porn often features attitudes and acts and behaviour that are sexist, racist, unsafe, disrespectful, dehumanizing, improbable, impractical, or impossible*.
Of course, indie queer-positive body-positive yadda-yadda-positive porn and erotica can also knowingly or unknowingly perpetuate sexism, racism, unsafe behaviour, etc etc.
And yes, outright fantasy porn with elves and orcs and +6 potions of testicular enhancement can also perpetuate negative attitudes.
In the same way, action movies can perpetuate negative or unrealistic ideas about violence, stoner movies perpetuate unrealistic ideas about marijuana, and even real unedited sports competitions can give aspiring athletes unrealistic ideas about what their bodies can and cannot do.
And that, I think, is why I think age ratings are so important - not because the sight of a boob will scar children for life, but because during your formative years, even overtly fictional or fantastical depictions of adult interactions can establish templates and standards for how people are supposed to behave.
So yes, dear readers, I'd like to reiterate that despite the lack of explicit gore or nudity, Leftover Soup is and always has been intended for readers eighteen and older - or the mental equivalent, anyway. Certainly, no one in the strip is intended to be a role model to be idolized uncritically and swallowed whole. Don't be like Jamie and Ellen, kids! Use condoms, even if you're on birth control and you're really really sure that neither of you have STIs and you really really love each other a whole lot!
For that matter, maybe wait longer than a month and a half in real time before hooking up with your roommate. Or, y'know, start at first base and have an actual conversation or two before moving to second and third.
But yes, Max does have a point. To return to D&D terms - sexual intercourse may be a Charisma-based check, but it's also something you can allocate skill points and feats towards, if you choose to optimize your character in that direction. It's safe to say Jamie's character sheet is different from Max's, and Max's would be different from that of a professional adult performer.
*Yes, impossible. Even if you're watching a video of naked people with no CGI or muppets, there's still such a thing as deceptive editing.