The guilds' feelings about their profit margins are irrelevant. The government would put its boot in their asses if they get in the way of such a massive strategic and economic boon as his duplicate potion.
It's kinda like the French guilds. They decided to screw around with the economy in France and essentially dictate it, such as prices and customers, and so the French government at the time dissolved them.
They can kick and scream all they want, but at best they have no power and will lose all of the power and wealth they want to keep. At worst, they'd get their necks laid on a chopping block as an example.