Lia Thomas -- the first transgender athlete to win an NCAA Division I championship -- is firing back at her critics ... saying a lot of them are simply transphobes who are "using the guise of feminism" to hide their true, hateful beliefs.
Thomas opened up about her detractors in a lengthy interview this week with Schuyler Bailar -- the NCAA's first trans swimmer -- and she said it's just not possible to claim to be a feminist but to also not support her when it comes to competing against biological females.