I sincerely doubt making crafting easier to level will ruin the game's economy. There are plenty of other things that affect the economy besides crafting. Drops from monsters and gathering perhaps play a far bigger role, but nobody seems to mind that too much when folks discuss battlecraft levelling.
If anything, letting folks level crafts for free from leves is a GOOD thing for the economy, at least as far as keeping synthesis actually profitable (Which I'm guessing is your issue, because the major legitimate concern over an increase in crafters is a decreased price of finished goods from competition). Guildleves allow players to level up their crafts without crafting oodles and oodles of trash.
The requirement to create so much random crap and find some way to get at least some sort of a return out of it is what leads to crafting almost never being profitable in any MMO: You wind up with far much supply than there is demand for, and players eventually wind up selling for less than it costs to make simply because they want to get SOMETHING for return, rather than just dropping the item on the ground.