Just in case anyone is confused, Psychohistorical Crisis is by Donald Kingsbury, not Isaac Asimov. To my reading, there is no suggestion in Second Foundation that Pelleas Anthor has the remotest interest in Arkady Darell, who is precocious but not coquettish. It's true that Lord Stettin has designs on Arkady as a potential consort but he's flagged as a bad guy anyway.
Also, it's worth keeping in mind that the older practice of looking at a young girl and considering her future sexual prospects as an adult was not pedophilia. It wasn't about wanting her at her current age, but about looking forward to when she'd be fully grown and eligible. After all, in those days, the cultural norm was to wait for sex until after marriage. So you could be in love with someone or engaged to them for years, but it would be taken for granted that sex wouldn't come into the picture until the right, culturally and legally approved time. So noticing a young girl's attractiveness or considering her prospects as a potential mate wasn't about exploiting her in the present, but about considering long-term options, making an investment that might take years to mature and pay off.
So we have the authorial intent. The question is, in Psychohistorical Crisis the author is condemning these practices or not? There are presented as simptoms of a decadent society or he wants us to believe this is the natural evolution of our sexual culture?
I think it's unhealthy to actively mine a writer's work for excuses to condemn the writer's morality. Yes, there are some writers who disappoint us when we learn of their real-life beliefs and actions (including Asimov's treatment of women, as well as Rowling's transphobia and Card's, well, everything), but it's not something you should actively start a witch hunt for. It's still a basic tenet of morality to give people the benefit of the doubt, to presume them innocent until the evidence compels us to do otherwise. If you assume the best of someone and you're wrong, that's on them. If you assume the worst about them and you're wrong, that's on you.
Writers and their stories are two different things. Stories are about characters in conflict, so naturally any competent story will depict beliefs and values different from the writer's own. Sometimes writers choose to write about protagonists they personally disagree with because it's interesting to explore their characters (for instance, Joss Whedon has said he disagrees strongly with Mal Reynolds's worldview and wouldn't enjoy having dinner with him). And sometimes a writer's work can transcend the writer's own limitations -- for instance, it's easy to read a lot of things in
Harry Potter as allegories in favor of trans rights despite the author's transphobia, and
Ender's Game is a powerful statement against the kind of xenophobia that its author now embraces.
This is because the meaning of a work comes more from its audience than from its creator. After all, something only has meaning if there's someone for it to mean something
to. That's what allows a flawed writer's work to transcend that writer's flaws and even become a powerful counterargument against them -- because what it inspires in its audience outweighs what the creator might have had in mind. But by the same token, if you're eager to read immoral or perverted meaning into other people's creations, that's probably more a reflection on you than on them.