You dont know very many MZ twin studies do you? There are at least a dozen. 1. You are probably citing the Bailey/Pillard 1992 study which was discredited by Bailey himself for the biased non-random sample. . 2. The Hershberger 1997 registry study had a 0% concordance rate for males and the Bailey/Martin 2000 registry study had a 0% concordance rate for females. 3. Since you know so much about understanding objective scientific studies perhaps you can tell us why in real science is replaceable except when it comes to twin studies?
How about the 1993 study from Arizona State University, Tempe that states "[The] findings are interpreted as supporting the argument for a biological basis in sexual orientation."