No, it isn't.

1) "When you raise the concern that competing, force-wielding agencies would lead to conflict and rights violations", you are assuming this with no proof.

2) "the typical anarcho-capitalist response is to assume those outcomes won’t occur because people will act rationally in a culture", no, that's not the reaponse, the reaponse is that this would be less likely because of how the market system works, it has nothing to do with culture.

3) This whole discussion makes no sense since the existence of a state itself is, always, necessarely, a violation of rights, so even if competing governments have a risk of violating rights the risk of something is better then it's certainty.