If I ever respond to a loser making stupid arguments on here it's purely for the lurkers. The real point of any debate, especially an online slapfight is to convince the onlookers. I know that no amount of unfun facts can convince a TRA, porn addict, or prostitution enabler to reconsider their views in one day, but it's enough to challenge curious followers who aren't hellbent on all their beliefs yet.
TRAs, of course, know this very well. This is why they have a strict no-tolerance policy for the fearsome "terfs." They know that no amount of bullshitting is going to convince a feminist, or even a GC person to move into lala land - but their worldview is so full of contradictions and inconsistencies that simple questioning will make it all fall apart for casual supporters. Ironically, the best argument a TRA can make is none at all.