Well, a villian who's sufficiently self delusional (and most of them are) could go back to deluding themselves as soon as their out of the lasso's clutches, though a part of them would always know the truth- making them even more tortured.
Also, I think Wonder Woman's usual careful about screwing with people's souls like that. Usually she gets the info and gets out, but here, Captain Nazi is threatening her people and she wants to make sure he never does that again. She knows doing something like this could easily make someone self destruct rather than see the light.