KnightoftheStar
Chieftain
On a related note, I think Mercantilism should be penalized after the discovery of corporation, since it's not realistic to have no trade with other countries. I can even say after economics is discovered the penalty can be applied, but that might be too soon for the mercantiles to switch. You can always aim for SC/communism if you don't want free trade and the risk of a great depression.
Once you hit all the bonus trade routes and improvements available at corporation mercantilism tends to lose its economic edge over free market unless you have multiple vassals or are THE game in town, I know in one German game I played I stayed with mercantilism up to the end due to multiple vassal states and ruling all of Europe, with all the infrastructure inside the Reich I didn't need much foreign trade.