I'll see if I can clarify.
Since being gay carries a social stigma, alot of guys do not want to be identified as gay. If they can find another "rough trade" man, then the less likely that the sex they have is "gay" identified (for instance, having sex with a flamboyant gay man would be gay sex).
It doesn't make sense to me, since having sex with the same sex is gay.
In South America, if you are having sex with another man, but you are on "top", then that is not considered gay. Being on top is considered more masculine, therefore, less gay, so the "top" doesn't have issues with having sex with another man. If you are the bottom, then you carry the stigma of being gay, therefore, less desirable for DL sex.
Clear as mud, huh?