Yaharog V'Al Yaavor

The Rambam in Yesodei HaTorah 5:1 seems to hold that one must give up his or her life for the aveirah of gilui arayos. The problem is that we learn that one must give up his life for gilui arayos from the fact that one must give up his life and not commit murder. By murder the halacha is that it is b'shev vaal taaseh, meaning since we cannot judge whose life is worth more, so don't do anything. If so, by arayos also the din should be shev vaal taaseh, and all by woman all gilui arayos are considered shev vaal taaseh, so why should she have to give up her life?
This point regarding gilui arayos is already made by Tosafos.
R' Chaim attempts to answer this question in his first piece in his sefer on the Rambam. Basically, R' Chaim offers two approaches. First, he suggests that even though by retzicha it's simply a sevara that one should not decide whose life to take, the question is how that sevara is transferred to arayos. By arayos we say that the maaseh aveirah of arayos is more important than the person's life. Thus, since it is a maaseh aveirah whether it is b'kum v'asei or b'shev vaal taaseh, so it becomes assur either way.
Then, R' Chaim takes it a step further. He suggests within the Rambam that even by retzicha this may be the case. Even by retzicha, the sevara of "whose life is more important" really tells us that the aveirah of retzicha can never be transgressed. Thus, if one could imagine a maaseh retzicha b'shev v'aal taaseh, one could not transgress that aveirah and would have to give up his life. R' Chaim just notes that practically speaking this won't occur because if one is forced by someone else to commit retzicha (meaning physically forced - like he is thrown on top of a baby), so it wouldn't be his retzicha anyway, but, rather, the one who forced him. Thus, in that case the person wouldn't have to give up his life.