Should transwomen be legally treated as women?
No. One's gender is defined primarily by one's chromosomes (X/Y vs. X/X), and one's consequent innate capacity to produce one type of germ cell or the other (sperm vs. eggs). One's gender is secondarily defined by one's hormone-induced physical development from pre-birth to adulthood. Transgendered people do not have either of such traits of the gender that they want to be, except perhaps in the case of the development of the brain. Therefore at most, a transgendered person could be considered a person of chimeric gender.