I agree that it is difficult and I have been there myself. The thing is - if it's a typical work relationship, it's theirs to do with as they wish, even if you built it. That is the difficulty of doing creative work for hire. I think it is a tight rope walk, balancing sufficient investment to do a good job without becoming overly invested. It helps me to think of everything in terms of a means to an end. I still feel the same emotional attachment, but I run all my actions through a filter of whether that particular action is beneficial. Writing such an email and sending or publishing it simply cannot ever do you any good.