Let's pretend that Negative ET's have enslaved humanity for eons and send down orders from the top of the pyramid on how to control us.
If positive ET's invade and try to free humanity the negative ET's simply threaten to wipe humanity out.
If positive ET's try to land, the negative ET's puppets (our world leaders) will tell us they are here to harm us and send the military's at them.
How can the positive ET's help humanity?
If they help, humanity dies.
Well. What if you infiltrated humanity with positive ET souls.
Millions of them all in one life time to push humanity to freedom from the inside.
Infiltration not invasion, my incarnated extraterrestrials.