The British opponents of the Corn Laws rightly understood that tariffs and other restrictions on trade are violations of fundamental natural rights, and that they privilege certain entrenched interests at the expense of everyone else.
In every trade, a person is giving up something he values less for something he values more. Every time a shopper buys any item from another person, he has improved his standard of living, and so has the seller.
The British complained of unfair competition from goods supplied by the American colonists. So the state intervened to manage trade and make it "fair." But the American revolutionaries saw protectionism for the scam it was, and still is.