He didn't stand to defend them, he stood to stop the King from doing something wrong. Although I doubt Caspius is in any kind of condition to recognize the distinction.
I would have to disagree. You stop someone from doing something wrong by telling them (verbal communication), with minimal physical interference (like Mathilda did.) Henzo, however, drew his blade and pointed it right at his own King, informing him he'd have to go through him first. His reason was inadequate, for if we look on the holy scale, I would think Caspius far outweighs Maria. That is defense, plain and simple
. I see it as such both OOCly and ICly.
If Henzo isn't banished, he'll be punished one way or another.