The real reason Nale destroyed Mallack (and why he died a true hero)

[Squire Doodad]

Nale is self-styled and unrepentantly evil. Not only that, but he aggressively prevents others from advocating for him (see: moments before death). Doing one thing that can be interpreted loosely as having a positive impact on the world for entirely selfish reasons does not erase a life of deliberate misdeeds.

I don't think he was preventing Tarquin from advocating for him. He was trying to disregard all of the "weak" rules his father had made for his party, and trying to spite Tarquin for not believing he could hold his own. He is arrogant and he is foolish and most certainly evil, but in that particular situation he didn't actually do it to prevent anyone from advocating for himself.