As far as I understand it, causality is just the relationship between cause and effect. If I’m right, saying it tries to avoid paradoxes is like saying gravity acts whenever someone falls off a cliff to prevent them from flying.
If I really needed to explain away time travel in this fic, I’d probably have a future Twilight show up and say “Whatever you do, do NOT use time travel. I don’t care how bad it is. Even if Equestria is going to be destroyed if you don’t. DO. NOT. MESS. WITH. TIME.”
Fortunately, I don’t see any situation in this fic where Twilight would even want to use time travel. Arguments aren’t one-time only things, you can always come back with another counterpoint later against a rational opponent who’s arguing for the sake of finding out who’s right, rather than to win social status or something. And any losses of social status that may occur in the fic are nowhere near worthy of time-travel to fix them, it’d be like cleaning a house by burning it to the ground and building a new one.
If you have an imperfect memory and you think they don’t, wouldn’t you want to pre-commit to attempting co-operation with any immortal entities you face, given they are very likely to remember you, even if you don’t remember them? This is of course assuming that most or all other immortal entities you’re likely to face in the Dilemma do in fact have perfect memories.