Biological men have a biological advantage in sports, especially those involving strength, speed or endurance - this is the reason why sex categories were introduced into sports in the first place, and why all men's records in directly comparable sports are better than women's, eg sprints and long distance running, swimming, cycling etc. Allowing transgender women to compete against biological women is unfair and takes opportunities away from biological women - the two potential solutions I see are either the invention of a third category to accommodate for athletes who do not identify with their biological sex, or having all athletes who do not identify with their biological sex compete in the male category.