It appears to me that the work of alien visitors here will in the long run 
benefit both Earth people and the aliens themselves. A win-win, as both they 
and we possess genetic flaws that require repair. In scientifically 
utilizing our genetic resources, the resulting offspring are or will be 
superior to both humans and aliens. What they are doing is an advanced 
application of genetic science - eugenics; controlled evolution.

They need us just as we need them, but in our relatively primitive and 
ignorant state most here do not see this, but either deny the existence of 
aliens or consider them a threat. If they were hostile to us, we would 
probably all have been exterminated by now. Chances are we eventually will 
be grateful for their presence and intervention. Were we crazy enough to 
begin a war that threatened us with extinction, they wpould probably 
intervene in some way - as they need us, even if as no more than lab rats.