because not executing your mafia member that day is also, in a way, an alliance, as the town will then give you a chance to win, and a pretty good chance at that.
Why are you giving me this lecture right now?
I perfectly understand everything you're writing here, and why you're writing it. It's because you're young, you'll calm down over time, you'll learn, you'll get used to it. It's the same kind of nonsense as "Morni is pretending to be Gura, why would he pretend to be Gura if he's not mafia? Maybe he just wants to have some fun and make the game more interesting," and that's even though I was "pretending to be Gura" even at the stage of choosing the role.
Besides, we all know who won in the end.