The choices are worded with obvious bias. Of course people want to be free rather than pay for another account but...

I think the benefit to being able to only master one craft is that then you as the crafter will become better known and sought after.
The market wouldn't be flooded with stuff that no one can make gil on.
Players would be less faceless. As of right now everyone can have 50 in everything, where is the fun in that when there is no individuality?

I'm all for Mastering One Craft.