While I agree that until her testosterone levels are lowered within a normal female range, she should not be allowed to compete with women, unless women competing in her events were allowed to dope. However, the bolded is NOT accurate. In Caster's case, while she may have XY chromosomes, her body is
insensitive to testosterone's effects. Androgen insensitivity syndrome or AIS can be complete or incomplete due to a malfunction of the SRY gene on the Y chromosome.
Every fetus essentially starts out as "beta female" with internal gonads and it's the activation or inactivation of anti-mullerian hormones that determines how these gonads develop (anti-mullerian hormone triggered by SRY gene to up-regulate androgen production causes the development of testes and destruction of the residual tissue that
would form the Fallopian tubes/ovaries). Due to some mutation, Caster's body did not respond completely, so while she has internal "testes" that may produce excessive androgens, the receptors on her body's cells don't respond as a male would in the presence of testosterone, rendering her effectively female. Even if Caster were to take in
additional testosterone via injections, her results as far as muscular development would never reach that of a man because her cellular receptors don't respond to androgens. In hormonal conditions such as PCOS in women, overproduction of estrogen can inter-convert this excess estrogen to testosterone quite easily which is what causes excess hair, amenorrhea, and male type central obesity in women with the condition.
A transgender female (MTF), would have both
normal responses in androgen production levels and and androgen receptor activity, thus making them effectively male. Sex hormones are weird and not exactly as cut and dry as they may seem. Testosterone and estrogen readily convert back and forth and levels that are too low or too high even in normal cisgender male and females can cause systematic issues.
The issue is that she is not genetically a woman. High testosterone in a woman is not equal to the testosterone levels achievable in a genetic male. This is the same argument that many have with transgendered women competing with genetic women. It isn’t discriminatory to acknowledge there are differences between men and women.
Biologically it isn’t the same. This isn’t a woman with abnormally high testosterone results this is someone who is inter-sexed displaying hormonal levels more in line with their genetic makeup.
No one is saying she can’t compete. She just needs to compete on a fair playing field.