That is an obvious conclusion that I have been saying for decades. But I am no Stephen Hawking, so no one listened to me

Even if they come with good intentions, the culture shock alone would be enough to kill us. And there is no ground to believing that they would come with good intentions. The only case that could happen is if they did not know scarcity. But scarcity and the fight for resources is what drives the evolution. With no scarcity, they would never have evolved beyond the level of pond scum, let alone develop interstellar travel.