What one character would have the bag space to manage every single profession?
My enchanter and jewelcrafter could never be the same character simply due to bag space.
I hadn't considered that at all. O.O
I think the theory is that an awful lot of people are already self-sufficient -- they just achieve it by having profession alts.
That's probably true, but I think Zachfu's right that the real problem is the people who aren't self-sufficient now, but may become so if they don't have to level alts to do so.
If every character had all professions, there wouldn't be much use for trade chat anymore.
Since when is trade chat used for trade? :)