Can we blame someone for making irrational choices during emotionally intense situations? Suppose that John was deeply in love with Joyce while Joyce is really using John for his money. It's obvious to all of John's friends, he is being used but he won't listen to reason. Is John to blame or is it his biological makeup to blame (or his environment) ? One can say that there are plenty of people who are able to snap out of these types of situation so why can't John, but I don't think it's that simple.
Try this out: We cannot blame John morally for the particular behaviours he exhibits while under the spell of the lovely Joyce; after all, he is not in control of himself. Nor can we blame John morally for being the kind of person who -- because of his 'biological makeup' -- is prey for Joyces. However, we CAN blame John for being the kind of person who falls heavily for unsuitable Joyces, IF we believe that the cultivation of the kind of person we are is in some measure in our control and the object of particular trends in our choices. John should have learned from his mistakes with the last Joyce; John should understand his own weaknesses and find ways to compensate for them, perhaps seeking counselling; John should learn to trust his friends advice; John should learn to read people; John should get out more. It doesn't seem unreasonable to ask these things of John's character, in general. Although, first, we have to get rid of Joyce.