I am sure there are some very nefarious goings on when it comes to Humans and all their experiments and power politics in this area. But to say as a blanket statement that all Aliens are good as you say is "Naïve".
I think based on what I have read and seen, the reason Earth hasn't seen its Humans eliminated is only because we are seen as a bit of the flora and fauna of the planet. And there is a directive, after all the wars conducted in the area by aliens - that planets can only be mind controlled and not OVERTLY controlled.
Then an Alien can say-- "oH we talked to the leaders of that planet and they said we could be there exclusively as their "friends". And what was discovered ? That yes, indeed, the United States signed a treaty with the Aliens (reptilians and Orian I believe) to say == sure come on in guys ! Do what every you feel like, but give us flying saucers !
The truth is always some where in the middle.
Either Greer is Naïve or he himself is mind controlled. Greer doesn't seem to be someone who is fooled easily so I'm thinking mind controlled - as it appears (by Farsight remote viewing) that, this is what Aliens do !!