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.
What's a reason that is politically and not against one's conscience? I assumed that one's political beliefs would also manifest in conscience.
The cold war has been over for a very long time. The whole process was reformed in 1984 by removing the mandatory oral hearing. Sources say that acceptance rate was above 90% after 1995. That's not good enough (should be 100%), but not terrible either.