I read the wikipedia page on Mafia…
Apparently, the Mafia are hidden within the civilians and pretend to be them. During the night phase, they get to pick a civilian to slaughter. During the day phase, all players vote on who gets killed, whether they are civilian are not (hopefully Mafia if you’re the majority).
So it’s kind of balanced…
Mafia: Smaller numbers, slaughter at night time
Civilians: Bigger numbers, votes on killed in daylight with Mafia.
Also, all the Mafia know who each other are, while Civilians don’t know who anybody is.