First of all. The author of the game, Crime, is already planning to add Futa, and they are a pro-LGBT, its up to them if they want to explore that route or not.
2nd. Even if he added it, you don't have to unlock the character. You can just ignore it, you know?
3rd. There is no harm if he added a femboy character. You said "There are plenty of gay games out there", well darling, there are plenty of straight games out there, you can play them if you want.