No. Fain can contaminate people because he has the dagger; it is the dagger. What Verin and Moiraine thought was incorrect; they were extending it too far. It is the one of things you may have noted in the books. Aes Sedai often believe they know more than they actually know. In other words, a lot of people believe they know more than they actually know. One of the themes I have running through the books is that whatever you think you know, some of it is almost certainly wrong, and it may even be the most crucial bit that is wrong. But even when you are aware that some of your information may be wrong you still have to go ahead and make a decision. You...you cannot afford the luxury of saying, well I don't know everything and some of what I know may be wrong, so I am not going to do anything, I am just going to sit here and wait and see if I can find out some more, because that only leads to sitting still forever.