It's entirely possible that there are ET's who are good, and those who are bad.
The Bible speaks of angels who are both good and bad ... when satan rebelled against God he drew a third of the angels with him. there was a great battle in the heavens , it could explain why Mars looks like it was inhabited at one point but looks desolate and destroyed today like the other planets. There may have been an age before this current one , prior to satans rebellion against God, were our planets were inhabited and thriving...after the battle satan was roaming the air between heaven and earth as the bible explains .... God created Man and set in motion a plan of salvation for the souls of his children who hear his call and know his name ... the others who reject God's call will be sifted out and seperated in this current age ....satan knowing this is happening would do everything in his power to decieve as many of Gods children as possible .... satan would probably go as far as trying to genetically engineer his angels to appear "human-like" if he could , so as to mingle with mankind in the flesh , which could explain abductions and cattle mutilations, etc ... it could all be part of a sinister plan towards an attempted deception by evil forces. You will know a tree by its fruit, if some abductees are being traumatized and used for attempted breeding of hybrids then that type of tree is not showing good fruit of a loving and caring nature. It instead shows signs of an evil nature who has bad intentions ... not many abductees have ever told of feeling any sense of love coming from a "gray" ... they only speak of being terrorized and traumatized.
The Bible speaks of the evil angels looking reptillian or frog-like ... yet Mankind was created in Gods image ... could the evil reptillian angels of satan be on a mission to try and cross-breed to create a hybrid "human-like" creation? Satan has always tried to mimic God and this wouldn't be a stretch to imagine.
Much discernment is needed in this field ... but like I say, there could very well be "good" ET's too ... the bible does tell of "good angels" fighting against bad angels in the heavens , fighting to protect Gods children here on earth as this "AGE" plays out to its ending with the return of Christ.
The Bible warns of satan trying to deceive all mankind right before Christs return.