If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn out well for the Native Americans—Stephen Hawkings
So here is the scenario. Aliens come to earth with three ships. The Nina, the Pinta and the Santa Maria. They steal all our gold and other resources. They give most of the planet something akin to small pox. They have sex wih our women. And they go away with syphilis. They ply us with booze. The move us off our land and replace it with alien oriented consumer models. We eventually get back at them by building casinos and fleecing the aliens of all their cash until they become a sickly, overweight and uneducated mass of organic life addicted to our media and fast food. Thus we eventually defeat them.