Oh, I definitely think it was understandable. I like Harriet Jones, and I think she made an understandable mistake. I just think the Doctor's reaction is also completely understandable.

That's what I really like about the conflict between the Doctor and Harriet Jones -- they're both sympathetic, and both points of view are understandable and defensible. It's left up to the viewer to decide on the rightness and wrongness of each character's actions. I like that the show wants you to question the characters like that, and gives you this moment of moral ambiguity right between the sweeping triumph and the happy Christmas meal.