No Evidence for Extraterrestrials?

I've been struck lately by academic scientists-- e.g. Harvard Psychologist Susan Clancy and Evolutionary biologist Richard Dawkins-- who simply can't believe or won't acknowledge that evidence of extra-terrestrials visiting the earth exists. It's really a stunning ignorance of even looking at or simply acknowledging the extensive evidence for an alien presence on our history. Now, either these people are intel agents, and are purposefully putting out disinfo to fool the educated masses, or they just have some mental block about getting into anything that smacks of "conspiracy". I don't know. I suspect the latter for Dawkins. On the other hand, Clancy specifically delved into the question of ETs in her study of alien abduction stories, and refused to admit any claim of any UFO or abduction was real. Clancy may well be intel. But overall, it's ridiculous and ignorant, to have "scientists" refuse to look at evidence because it is controversial.