You haven't followed the situation in Ukraine, have you? There are always people who are willing. You don't need a lot of them.
And the orders are given in a way that sounds convincing. They aren't going to say "there are 2000 women and children unarmed in a park doing nothing. Go mow them down." They will be told that armed thugs and terrorists are destroying everything and killing innocents etc. And you gotta go squash it before there is nothing left of the city. Who could argue with that?