I don't get the should at all, or the automatic judgment that this particular thing is something that no T should do at any time. Are there really absolutes about things a T can or can't say to be therapeutic?

If I were going to come down on a side for what a T should or shouldn't say, I would come down on a more free or open communication with clients. Exceptions being requests for sexual favors or turning a session into being about them.

As to the specific content that was mentioned, it would seem important to me for a T to offer a perspective that doing X thing doesn't make someone a "monster." A client thinking she's a monster is probably engaging in some kind of distorted perception, and one of the things T's do for clients is to give them feedback about how they think about something, including themselves.