The "forcibly taken" is an angle that lot of Netorare takes, but it is "Loss" that is the big definition I think loss is twice a intense if you endure herculean trials trying to "save" the girl from the guy who is extorting her into being his sex slave, just to be told at the finish line that "actually she loves him now, not you, so she is staying".
The big arguments stem from the point you can't loss what isn't yours to begin with, all those Anti-NTR folk crying that all women are their LI's because they want them, is right up there with the those who claim various celebrities are their soul mates, if they can't have them nobody can.
As for the courting argument, that has a certain amount merit if the girl gives fair indication that she wants you, in the case of the mayors son, that really doesn't apply because neither of the women wanted him or lead him to believe they wanted him, he was simply a wannabe rapist in waiting (rape isn't NTR either, the LI has to choose the other guy over you, having a LI raped is a traumatic event but you still have each other after)