As you said, you can only object if it goes against your conscience, but if you are against it for political reasons (e.g. you don't think its worth it to die for Germany), that's not a valid reason and your objection will be denied. They were also incredibly strict during the Cold War, only easing off a bit afterwards when they wanted a smaller military.

On the contrary, it says that even if you object, they can force you into "alternative service" without the use of arms. So they make you a soldier without a gun, or rather - a state slave.