Contrary to what writers of mystery novels and the standard cops and robbers scripts present, motives are as varied as the individual. Human lore portrays murder for vengeance, for sport, for power or money, but seldom if ever portrays murder for desensitization or simply to attain peace and quiet. Most murders, few of which are ever solved, are committed by those solidly in the Service-to-Self or moving in that direction. They understand they will be living with their own kind in the future, segregated by orientation, and that the more ruthless will rule those who hesitate. Many murders are also committed simply to rid oneself of a temporary annoyance - the loud mouth at the bar, the aggressive driver weaving in and out of traffic, or the demanding shopper never pleased with what the clerk brings forth. Motives are complex.
What can be said about ultimate alien agendas is that they can be cleanly divided by orientation. Those in the Service-to-Self may promise creature comforts but their ultimate agenda closely resembles bondage. Those in the Service-to-Others may tell their contactees hard facts about the coming Earth cataclysms but the ultimate agenda is empowerment of the individual and safe passage. Is this not the case in human society? Are the parents who insist that their youngsters do their homework and get a good night's sleep being cruel or caring? The ultimate alien prize is the human soul, which will incarnate in this or that orientation repeatedly.
As ourselves, the Zetas, will be incarnating on Earth as the Transformation progresses, we have a particular interest in seeing the Earth and her people evolve, rather than be despoiled. You have a beautiful world, a glorious world, and are spewing poisons into it and decimating species with no thought of tomorrow. Preserving Earth for the future is most definitely one of the Zeta agendas.