If a thief wants it, they'll get it. Things such as wheel locks, car alarms, and "The Club" act as a deterrant so that...

1) If they're lazy, they won't go for it or...
2) If they want it bad enough, you make them work for it.

It just makes them work harder for something, that's all. If you had two identical cars parked next to each other and a thief walks up right in the middle because he wants to steal one of them, do you think the thief will steal the one with the alarm/wheel lock/club? Or the one that doesn't have anyone of them?

Just my opinion, of course