Sperm,eggs, or skin are not human life.
By whose definition? Yours?
Sperm or egg cells are not human life by the definition that a zygote, or a fertilized egg, is objectively the beginning of human life according to biologists. The formation of any viable human begins at conception which is the joining of a sperm and egg cell. Skin cells cannot engage in fertilization.
A skin cells contains all the same genetic material that a fertilized egg does. It also contains the exact same ability to think, feel, interact, feel pain, or indeed feel anything at all - i.e. none. We can also take the genetic material from a skin cell, place it in the right conditions, and use it to grow an entire organism. Why is one human life and the other isn't?
You're using the word "think" loosely here. Skin cells responding to stimuli is an autonomous process that doesn't involve any sort of thinking. Because a skin cell can't think, it can't respond to pain either.
We can also take the genetic material from a skin cell, place it in the right conditions, and use it to grow an entire organism. Why is one human life and the other isn't?
This is like saying a tumor is human life. A mass of skin cells do not result in the formation of a sentient being. A zygote does.
In developmental biology, fertilization marks the beginning of a human's life since that process produces an organism with a human genome that has begun to develop in the first stage of the human life cycle." Three-quarters (75 percent) of biologists agreed with that statement.
Of course they did. I agree with that statement. It doesn't change the fact that a fertilized egg is no more a human being than a skin cell is.
The idea of calling a zygote human life is to apply an objective standard to abortion. I am not one to argue that a terminated zygote is more tragic than the termination of a 8.5 month old fetus in the womb because the latter is devastating while the former does not create the same emotional impulse. Clearly there are differences between a zygote and a developed fetus and you can rationally reason yourself through the physical differences. I tend to be pro-choice but see the logical flaws in supporting abortion and struggle with the rationality myself.
If you support abortion and want to make an objective argument, you can't arbitrarily assign value to human life based on development or based upon your feelings of the context of the abortion. Many pro-life individuals believe abortion is okay anywhere conception to before "X" weeks. But in this instance, they are arbitrarily creating standards for when abortion is okay and when it's not okay meaning that you cannot objectively say human life has an innate value. In addition, you need to ask yourself this question. For example, if you believe after 26 weeks abortion is not okay and anything before is all right, what makes the fetus any less of a human being before 26 weeks versus after? Sure, you could point to physiological and anatomical differences but major development of organs already happened within the first month of conception. Human life is in fact human life with or without certain anatomical features. So, there's issue in assigning arbitrary weeks as a cut off for an abortion because it's impossible to objectively articulate at what point the "clump of cells", as the pro-choice crowd calls it, becomes worthy human life.
This is wall that separates pro-choice from the pro-life crowd. Pro-life individuals believe that human life objectively has innate value and human life begins at conception. Thus, any form of termination from conception is ending innocent human life. As someone that's pro-choice, they're not wrong in their line of thinking. I just reject the notions that all human life has innate value.