I agree with what 3point1 said, firstly - clothes were clothes, they were not gendered colours in the 1970s, i had things which could do a boy or girl. Whereas now, clothes, toys, etc define boy or girl visually.
I don't know enough to say, but if gender dysphoria is something people are born with, isn't that like being on the autistic spectrum (which I am fairly sure my DS is). In other words, it is neurological and developmental rather than a mental health illness like I am depressed.
Not being accepted for who you are, or being pressured to conform may cause mental health problems, but that is different.
Even if one accepts (and I think this acceptance was the starting point for the trans* movement, and I am not disputing it) that gender dysphoria is a condition from birth, this does not mean a boy is a girl and vice versa. They are a person with a specific condition.
The debate is how individuals and society respond to that condition (thinking beyond male and female to a third or mixed gender with separate needs; or by simply taking the path that well, this person can 'become' the opposite sex through a process of transitioning). The process of transitioning only is possible in a society with sufficient knowledge of hormones, surgical techniques and finance for this (as well as permissive legislation), and where the outward signifiers of male or female are not genitals (in public space) but clothes, accepted gender roles and behaviours.
Secondly, what is on the table is now a long way from individuals with body dysphoria. It is about anyone who identifies as the opposite 'gender'. You cannot identify as the opposite sex because you are born with certain reproductive organs and that is how bodies are sexed. The male-female reproductive distinction shapes experience. It defies logic to say you identify as the opposite sex; and female separate spaces are about sex, not gender (which is a construct); women's issues are about sex, not gender. So, even if people want to identify as the opposite gender, they still do not have the same needs etc as people of the opposite sex.
Which brings us to the point of contention - the fact that the dominant sex (male) are using arguments about a socially constructed edifice (gender) to erode rights and spaces of the not dominant sex (female). The latter experience violence, discrimination etc on grounds of their sexed bodies.
This is rambling as on phone. I need to work out how this understanding has developed in less than a couple of decades.