Why Androids are differ from human

According to Existentialism, the most important consideration for individuals is that they are individuals—independently acting and responsible, conscious beings —rather than what labels, roles, stereotypes, definitions, or other preconceived categories the individuals fit . People should be exist at first, and then during their life process, their essence will be determined through their own behavior and thoughts.
Whether androids are exist is a problem. If existence means life, androids should be exist. They are built like real human in biology. By contrast, if existence means individual identity, androids should not be considered as existences. In the novel, androids are not admitted as "individuals". Human call them "it", and those who want to be an existence (be admitted like human) would be killed by bounty hunters.
Another thing that androids are differ from human is that androids do not fit in the concept of existence precedes essence. Androids in this novel are set as servants of immigrants to Mars. Before their "existence", their essence have been determined. Fake memory can be embedded to androids (human can not embed fade memory) and build their essence. Rachael thought she was the niece of Eldon Rosen and worked hard for the Rosen Association before Rick asked her to take the Viogt-Kampff Test. Because of the fade memory, she believed that she was a real human, not an android. So she worked hard for the Rosen Association's interest. Her identity, or essence, is born with her and is not determined by herself.

Or maybe Rachel can seek her essence herself. Although she acts quite professional when she is dealing with the business with Rick in the Rosen's Association, she offers her help to Rick to kill the androids on Rick's list. According to what we have read, this might be the action of her own will to find the sense of her life.

Very excellent ideas, I agree with you. We ought to consider this problem critically, as there may not be a definite answer to this question. It depends on how we define the words 'existence' and 'essence'. From my perspective, the androids may indeed have a kind of 'essence', but different from that of humans, their 'essence' are not create by themselves. Instead, the designers determine the robots' essence and that is how human distinguish from androids. If someone's mind, personality, memory are totally created by others, we definitely can not agree that he or she has essence, although physically exists.

It's quite interesting that Cindy brings up a topic of "individuals". She argues that people should exist before their essence, and it's why they're human. Since Androids don't have the individual identity, they can't be called exist. I have a slightly different idea about this topic. I think that Androids have the individual identity, at least, to some extent.

There're two issues about it. First, we can't deny that Androids have individual identity only because their identity is not that explicit. For example, Polokov chooses to hide under the cover of a cop to keep him safe, while Luba Luft thinks that being a celebrity is the safest way. Thus, we can illustrate that Androids have personal ideas and these ideals vary from one individual to another. We can argue that these identities are affected by planted memories, but Human's identities are also based on their memories. We can't deny the real identity only because that their memories are "fake", or we say that their memories are fake. Whereas since they have memories and they live on it, I don't think their memories are that fake.

Second, it's hard to tell who is fake and who is not. Cindy argues that Androids "do not fit in the concept of existence precedes essence". Whereas this concept is based on human's point of view. However, we can't argue that our concept is the only one that's right, force other creatures to fix in our concept and judge everything based on our concept. For example, some people think that marriage will still work well without love between a couple, while others argue that marriage has to be based on love. It's the same deal with the existence of Androids' individuality. We are like the people who argue that marriage has to be based on love, and we argue that existence have to be based on real memories. However, we don't have the rightness to argue that the Androids aren't real because their memories are fake. In addition, the idea of reality are also based on in what perspective do people look into them.