//I don't see how it's possible to "choose" gender.//
It is because the term is now largely meaningless, Tora.
I don't really care how people dress, how they behave or what they call themselves. They can call themselves a horse for all I care, so long as they don't try to enter the Grand National. But, except in very rare circumstances, and certainly not on a simple whim, one cannot change one's sex. When men start to encroach on women only spaces and participate in women's sport, that is a step too far. I note the UK government says it has concerns about the legislation and could seek to prevent it becoming law by blocking Royal Assent. I don't hold much of a candle for the current mob in Westminster but in this instance I hope they work well to thwart this most ridiculous idea from the most absurd leader of the UK's most Rotten Borough.