What makes people want to take jobs where they are mindless zombies?

Not to offend anyone, but there are people that like to think and there are people who don't care to think. Some thinkers, like artists, except for very few are poor so I can obviously see why you would not want to be an artist. But what makes people want to do jobs like police or military where they strictly follow commands without being aloud to think. If something is against the law they arrest the person, without thinking if the law is just or not. You go to war, they tell you where to point and what to shoot, but dare you express any opinion about why you are there. I just want to know is there some gene that makes people not care about having there own opinions?