Yeah it's understandable and it's an issue in a lot of games, mostly shooting ones. Everyone has a whole army of goons ready to murder you and you just one man army through all of them. Where do the bad guys recruit all these folks? It's an issue with the GTA games too, but at least they're deliberately over the top so while it's still a bit ridiculous it's not so bad, but for a more grounded series like Mafia it's worse. I guess the developers don't want games boring where you only kill a handful of guys, but surely there's a way to have a good mix of realism and fun. Still, try out Mafia 2 some day. It might be the best story wise.
http://i.imgur.com/hslUvRN.jpg
When I sin I sin real good.