Danny is afraid the Doctor will push Clara past the point of no return. He worries that the Doctor is so caught up in the big picture that he sacrifices people to achieve his ends. Just like a senior officer would. While he may be justified in this fear is it ok for him to issue an ultimatum to Clara over it? It is Claras choice to follow the Doctors orders not his. Danny sees himself as her white knight but is that what Clara wants him to be? Does she want to be rescued? Perhaps there was a moment in Dannys past where he desperately wished for a savior and did not find one. Danny doesnt trust the Doctor but it is uncertain whether he trusts himself either. There are indications that Danny may have had a difficult choice in his past. He may have held the power of life or death in his hands, and he may not like the decision he ended up making. Unlike the Doctor, he didnt get a do-over.