In order for the wolves to win, all the villagers need to be dead. In order for the villagers to win, they need to take up 50% of the population.
The only time a random kill is desired is when it is more likely to hit a villager than a wolf - which would be never, as the villagers would've already won by that point. Plus, random night kills would just shorten the time needed to find the villagers. At 22 players,it would take us 15 days before the villagers won. (21 starting wolves - 15 wolves = 6 wolves; 1 starting villager + 5 villagers = 6 villagers)Every additional wolf death from a night kill drops that number roughly by one day.
Please note that if the person with the night kill is certain that someone is a villager, or at least reasonably certain, then that heavily factors into things and will easily make it a good idea. How good depends on how certain you are. (and if you are correct, of course)
Yay maths for the second day in a row! This is apparently becoming a habit for me.
Note: Some bad math up above, as I forgot to include the lynchings. We should expect to have 9 days, at the least, to locate the villagers; this assumes a worst-case scenario where only wolves get lynched each day. Regardless, the point still stands; killing an additional wolf each night speeds things up, and you are much more likely to hit a random wolf than a random villager, especially on the first day.