Life soon becomes very hard for people like that. A guy I knew at school was all set for the army - was in the cadets, had really shiny boots, knew all the lingo and loved reading about war. But then it turnned out he thought he was cleverer than his superiors and that an independant mind is useful in the army. It's not. What the army needs to do its job well is people who will unflinchingly and reliably carry out orders, without thinking about the consequences. Having your own ideas is not just 'being cheeky', it's insubordination and they do not like it. He quit half way through basic training.
IMO, the perfect recruit is young and innocent, without a well-formed worldview or political stance - fresh to be molded into a soldier. If you already have your own ideas and beliefs that won't be swayed, then the army is not for you.
Of course I'm not a soldier, so anyone with experience feel free to correct me.