If your state requires you to have 2 license plates and your vehicle came with only one when you bought it then how do you fight a ticket in court?

I suspect you're screwed. Save your money, pay your fine, move on. It's the owner's responsibility to properly display license plates, and if you can't because you don't have them both, it's up to the owner to go to the appropriate authority and fix it. This assumes that you mean that it's registered in your home state, and your home state requires two plates. If it was legally registered in a another state that doesn't have two, but an over-zealous cop wrote you up for it anyway, that should be a slam dunk: what you were doing wasn't against the law.