Scientists have discovered years ago that with technology, every cell in the body, especially stem cells, can become sperm or egg in laboratory. They have done this with mice. They have taken cells from a "female" mice, stem cells which differentiated into sperm cells, and fertilized the eggs of a female mice with the sperm.

If it is the case that all cells, especially stem cells as they are the body's raw materials differentiating into any cells, can become sperm or egg, doesn't that mean there is no "just male" or "just female", and everyone is already both male and female?

Because apparently all it takes for a currently female human to create sperm and as a result become a male for producing sperm from their own genes, even if artificially, is technology which turns stem cells into gametes in laboratory.

And all it takes for a currently male human to create eggs and as a result become a female for producing eggs from their own genes, even if artificially, is technology which turns stem cells into gametes in laboratory.

I don't see how this is not the case that everyone is already both male and female when every cell has the potential to become sperm or egg.

During the natural embryonic development, stem cells differentiate to become sperm or egg. That's the exact same step they repeat in the laboratory, taking stem cells of a female and making them differentiate into sperm (which turns the female into a male for the very fact of producing sperm, even if artificially), and taking stem cells of a male and making them differentiate into eggs (which turns the male into a female, for the very fact of producing eggs, even if artificially).

This dives into philosophy, a little bit. We could go further, why is it that a heart is different from a kidney, an arm, an eye, a brain, etc, when in natural embryonic development, the same stem cells differentiate to give rise to all mentioned organs? Every organ comes from the same origin, the same stem cells, so why do we consider them to be different from one another? Why do we consider there be a "heart", "eye", etc separate from each other, that are their own things?

There are many articles on this, though I have summarized them in a less misinformed way (these articles tend to spread misinformation, with their wrong wordings, e.g. claiming two "females", two "eggs", or two "males", two "sperm" create a zygote, eventhough it's actually a sperm and egg creating a zygote, and one of the two "females" becomes a male, or one of the two "males" becomes a female as per the definitions of male and female): https://www.nature.com/articles/d41586-018-06999-6

https://www.nationalgeographic.com/science/article/news-gene-editing-crispr-mice-stem-cells

https://www.cbc.ca/news/science/same-sex-parents-mice-1.4860149

https://www.inverse.com/article/49792-can-two-males-or-females-make-babies

https://www.dailymail.co.uk/sciencetech/article-6265453/Hope-gay-couples-want-children-mice-two-MOTHERS-born-China.html

https://www.bbc.com/news/health-45801043

https://www.thetimes.co.uk/article/no-father-necessary-as-mice-are-created-with-two-mothers-2vskf8w58

https://www.telegraph.co.uk/science/2018/10/11/needs-men-first-mammal-born-same-sex-female-parents-gene-editing/

https://www.technologyreview.com/2018/10/11/139840/chinese-scientists-have-created-mice-that-have-two-moms-or-two-dads/

And I'm sure there are more articles out there on this topic.