The taxes on sugar have nothing to do with corn. Corn producers do not need HFCS to stay in business, they have ethanol when they need a subsidy; less than 5% of US production goes to HFCS, but the rest is basically split 50/50 between animal feed and ethanol.

Sugar imports are taxed so that US producers (cane in FL & LA, sugar beets in the upper midwest and upper great plains states) do not have to compete with cane sugar from Brazil and Mexico. It is as simple as that.