I don't think there is. Your fellow progressives obviously do.
The relativism of liberals should mean they have a problem with gayness. Think about it, what is the evolutionary advantage to being gay? None what so ever. Evolution is the holy grail of the liberal left yet when they say gayness is natural they argue against evolution. Evolution's "function" is to continue life, usually a more adapted life. Gayness does not fit that definition, the liberal left argues against themselves.
That said, I don't really have a problem if the liberals want to do things that are unnatural that is their business. But don't even try and convince me that the anal orifice was ever created, through evolution or design, for anything other the defecation.