What would happen if aliens came to earth to debate?
Most importantly, what will we argue on?
I doubt our political system, LGBT rights, gender equality, or the migrants crisis will pique any interest or concern. Maybe, we choose to argue on religion; both parties [assuming these aliens don't have some magical insight or facts to back themselves up] do no more than speculate in this area.
Every religious belief is as feasible as the next, so why not understand the belief system of creatures that lived and experienced totally different things to people in Earth. What if these aliens had a life span of a mere eleven years, or on the contrary are immortal. The idea of immortality on our planet seems so far-fetched, but in other planets evolution might have progressed so far, that life-spans are longer than the existence of our universe, or damaged cells can be repleshined with minds.
Truly, if these aliens had the capability to travel to our Earth then their technology is most likely to be severely better than ours. On the topic of religion, there would be no winner. But, humans as a species will gather priceless insight to advance the human race.