One of the arguments often presented in the old thread was that if Spock slept with Mary Jane, it would constitute rape, as she would not be willing to consent, since she didn't know that he was really Peter Parker. That got into a side argument about whether it would be rape (Some jurisdictions, although not New York, consider it to be rape if one person impersonates another in order to sleep with a member of the other's social circle.)
One argument was that the specter of Spock seducing Mary Jane should not be raised, because some people would interpret it as rape, and there is no place for the hint of that in a Spider-Man comic. I think the problem is that it's crippling for fiction if writers aren't allowed to hint at the possibility that specific bad things can happen.
There also seemed to be concern trolling involved in the old thread, with at least one very active former postere who didn't like the current Spider-Man comics pretending that this one possibility was the one thing that bothered him.