No matter how human a machine may seem it will never be a human being. They lack something within their great intellect that keeps them from understanding and becoming human. They do not care for their own kind and would give up other androids to better their own lives. They feel nothing, it is all made up and based on circuity. They toy with living beings and are doomed to die before anything alive ever does. They are not the same as humans and they will cause harm just by being near humans.
Rachael Rosen has toyed with Rick from the time they first met, passing herself as a human, making rick think that his test is wrong, telling him that he needs help to taken down the type 6. She then plays him with the night they spent together which leads to rick being even more uncertain that what he does is right. She lies about helping him, and then goes out of her way to hurt him (198,199,202). The problem is why she did it. Was it because she felt betrayed about Rick not loving her before his wife and new goat?(202). Or is this a lack of empathy for animals and humans that all androids lack? Maybe she was just mad at rick for not failing to break down like all others but one had before him. Perhaps she just wanted to get back at him for whatever reason, such as their talk in the hover car. Also it has very little to lose, she will live only for 2 more years. (197). It is owned by the Rosen Corporation so she is outside of his reach with the law and he would be hunted if he kills her (200). Rick on the other hand will mourn the loss of an animal, something she cannot. Androids are a mistake, they know too much about humans but cannot be them so instead they torment them and their humanity. They use human feels to get ahead when dealing with humans in any way they see fit.
Androids, however can make mistakes, around those who they believe lesser themselves they show their true self. They do not feel the need to follow the rules set by humans because they are not humans. They do not believe in the theology of humans and fail to understand why people would even after shown that it is a fake. (209,210,211,212). They do not care about living things and carry out experiments on living things. (209,210). Their minds, their processors are not capable of understanding life. They are flawed in that regard, they live for 4 years and so have no appreciation for it. Also they think they are better than humans and in the end that is what killed them. Their belief that they, things that live for only 4 years are better then something that lives for 80 year, can grow, learn and has been around for thousands of years. Humanity is strong, they have managed to live past the loss of their home world and even the wasteland of it. What hope can walking computers that break down in a few years have verse something like that.
Humans make mistakes too, many of them. However they often have time to fix them or just to move on. They destroyed their own world and fled to the mars, a world that does not want them. They made machines that are more flawed then themselves and that kill them. They believe life is sacred but do not care about the life the created. They hunt their own creations to the ends of the earth. Rick almost breaks downs several times over all this questions and more. Maybe he did break down in the end. Saw things that were not there or maybe he reached a point where everything is clear to him. Maybe now he is better then what he was before. (220-222,230-232,235)
In the end, there is nothing certain.