This is fair, because you're using the technique to redirect us back to the original morality issue.

But i also don't think that MBlume was completely evading the question either. The question was about ethical principles, and his response does represent an exploration of ethical principles. MBlume suggests that it's more ethical to sacrifice one of the lives that was already in danger, than to sacrifice an uninvolved stranger. (remember, from a strict utilitarian view, both solutions leave one person dead, so this is definitely a different moral principle.)

This technique is good for stopping people from evading the question. But some evasions are more appropriate than others.