Why can't we decide if tomatoes are fruits or vegetables?

It looks like a vegetable, but it's classified as a fruit. Or is it the other way around? The tomato is technically a fruit since it protects and contains the seeds of its plant, but according to a Supreme Court ruling, is is classified as a vegetable. 

Why? The Tariff Act of March 3, 1883 required a tax to be paid on imported vegetables, but not fruit, and they didn't want any tomato farmers going untaxed.