I loathe protectionism and the sugar lobby seems to have garnered more than most industries.
When I lived in Germany a woman I there knew wanted American sugar because she found it better to cook with. I have no idea whether it was or wasn't better, but I do know that sugar can come from different sources and be produced at different grades (and different consistency within those grades). Furthermore, health standards vary from one country to another.
I suspect that imported sugar would not be identical to American-made sugar, and - were price to be the main consideration in its importation - generally inferior.
Protectionism is bad for the market and bad for people. But not as bad as, for example, tainted baby formula from China.