Unfortunately, this division is connected to the old Liberal fear of world over population. The bogeyman never came home to roost but the fear is still there. By definition, homosexuals cannot reproduce biologically, thereby satisfying some of the classic Liberal fear of world overpopulation. Those who oppose it, are pro-life for the future.
Transgender, takes population control to the next level, and is becoming another world wide fad. The idea of mass sterilization used to be discussed, but that was considered too harsh and would be resisted. However, if you can convince people to choose sterilization, such as by gender reassignment, then is not exactly cruel, especially if you throw in free makeup kit.
Abortion speaks for itself in terms of population control. Pro-life is connection to the future of life, and addresses those many things that try to game natural reproduction.