I hope you won't take offense at this because I don't mean you any:
What evidence beyond "sightings?" What secret things do "some" know that the public doesnt'? How do you know? Really, doesn't matter what scientist or clergy or anybody else think about something they have not met or touched or experienced. There are either aliens or there are not. Right now there is some "evidence" that something is going on. But, it's not known to be this or that. So, again a soul sucking demon and a spaceman/woman have the same standing (imo) I don't think either is exactly what is happening now. But, I have seen "somthing" in the sky on one or two occassions that didn't "fit" into what I thought should be "up there." But, it could have been military, or a satalite or with my eyesight I could have just "thought" I saw what I think I saw.
Or it could have been a craft from another world or dimension. I remain open minded but this "proof" just hasn't (imo) revealed itself as of yet.