Those who oppose the inclusion of trans women in women's sports argue that trans women have an unfair competitive advantage and that as a result they will take away opportunities from cisgender athletes. According to the NCAA, these assumptions are not well founded. Moreover, there is a lack of scientific evidence that conclusively demonstrates a direct link between testosterone and athletic performance.

Athletic performance is influenced by a number of factors, including hormones, but also other things like coaching and training, psychological makeup of an athlete, access to resources and equipment, among others. Attempts to ban or limit the participation of trans athletes are not based on science. Instead, they are rooted in societal and cultural definitions of what constitutes gender or what defines a woman. Such questions matter because sports are organized based on the belief of natural differences between men and women, and they are sex-segregated as a result. Yet, this ultimately leads to the discrimination of athletes like Thomas.