It's unfortunate that gender issues is a political issue. There is a tremendous wealth of knowledge that the common folk is not aware of that may give them a false premise of sex and gender that they should not be influencing policy on this front. It's easy to think gender is entirely a sociological concept and sex is a simple as the equipment between the legs, but reality is nowhere near that simple. There is a tremendous amount of biological influences between sexes that influences cognition and behavior. The obvious ones being the hormonal ones. Even still in utero, a male baby is exposed to a significantly higher amounts of testosterone in the mother's womb. This results in many measureable effects, not just on sex organs, but in structures in the brain. One such structure is the aptly named sexually dimorphic nucleus of the hypothalamus which is twice as large in straight men as it is in women and gay men.
https://en.wikipedia.org/wiki/Sexually_dimorphic_nucleus
The effects of testosterone on behavior is well studied. Even chimpanzees show gender preferences similar to ours in toys. Female chimps prefer dolls while male chimps trucks and cars. It's obvious that chimps would not have the same sociological constructs of gender as we do, yet they show similar gender behaviors. Further solidifying a causal link between the biology of gender and behavior is female monkeys with congenital adrenal hyperplasia that elevates their testosterone to levels of males show similar gender preferences as male chimps. They prefer the same toys and engage in the same rough and tumble play. Testosterone is known for masculinizing behavior - aggression, competitiveness, development of strength.
The effects of raising someone under the wrong gender than the masculinization processes during development can be devastating. One such case is the boy named Bruce who had a botched circumcision and the doctor decided to give him gender reassignment to a female and have him raised as a girl. This made a lot of sense given the dominant belief at the time is that gender is entirely sociological. Bruce never felt right as a female and often showed male interests and activities and never considered himself as a boy. He was not accepted as a girl by his peers. At the age of 14, he found out about his history and reverted back to being a male. However, the damage has been done. At the age of 38, he committed suicide.
http://www.dailymail.co.uk/news/article-1332396/Bruce-Reimer-Tragic-twin-boy-brought-girl.html