Of course it can be one error and you're out. Or one doctrine you disagree with and you're out. If you're Catholic and disagree with the contraception ban, you can disregard it at your own risk (of eternal damnation, I suppose), but you don't have to choose between that and all of your friends and family. But if you disagree with the blood ban and accept a blood transfusion, or even tell others that it's okay to do so, you will be expelled. If they can establish that you took blood, they won't even hold a JC to see if you really want to leave. It's considered an automatic disassociation. Same with joining the military. A friend of mine from growing up kind of faded, but then joined the military, and he was DF'd (technically DA'd, but really what's the difference) without a judicial committee.
Technically it was his choice to join the military, but the choice really was between blindly obeying every rule and doctrine or having your family and friends.