 Because we don't know what they're like, you fool. And we can't take a chance. We can't trust them the fraction of an inch. Sure, I know. Let's try and find out all we can about them. Let's meet. Let's try to be friends with that ship out there. Well, we don't. And you realize why? Because they have locators. Because they might trace us all the way back home without our knowing it. And we can't risk a non-human race knowing where Earth is unless we're sure of them.