Welcome to the JavaRanch, Paul!
I never have gotten as deeply into Seam as I should, but the main reason why you shouldn't bind Domain Model objects directly as
JSF backing beans is that it's too inflexible. If you're only going to use the entity as a single, immutable reference, it works, but when you start talking updating - or worse yet, switching the backing bean to a different instance of the same entity - things start going downhill in a hurry.
J2EE is not really designed for cheap monolithic development. That's what ASP and PHP are for. J2EE works better when you have a large, complex design and you want to implement it in small, easily manageable pieces. Lots and lots of pieces, sometimes, but the important part is that they're all relatively simple, so when you dump them on the next trainee, he/she won't have to spend a week figuring out what all the ramifications are.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.