If they could understand our language, why would it be stupid to think they could be nice. I'm sure a lot less dogs and cats would be killed for food in China if the animals were able to have a conversation with the Chinese.
How many nations have been conquered while being able to communicate with one another, easy answer.... every single nation on this planet and billions have been slaughtered. Thanks for theory but NO THANKS.
If they are supreme beings they may view us like animals, if they have been watching us they know how barbaric and cruel we are, If they are looking for anything on this planet it would be nothing more then our resources; being light years ahead of us in technology we would contribute absolutely nothing to them.