It may be fictional but Itadori is still a minor, thick and through. Yes, fiction strays from reality, their two separate things but if you have this portrayal over fiction then your inner thoughts about reality would be quite the same. The same goes for people who sexualize lolis or give them sexual designs in general, yes in terms of age they are probably a lot older. But that is still a child body and if this is your open thoughts about fiction then your inner thoughts about reality would line up, even if you say you don't agree with it, you know you tolerate it but you wouldn't say it since in reality your thoughts would be deemed as horrible and you would be harassed for it. So subconsciously you keep it to yourself since you have seen and adapted to society's viewpoints. Maybe I should become a psychology major...
and again anyone who support this, is weird and disgusting you should go on a therapy if you like to see minors who are getting sexualized with a much older man...:/