I decided to allow human/alien crossbreeding, and even gave it an explanation for my alien world *tl;dr warning ;)* :
Human/Nameless-Species crossbreeding is as complex as it is controversial.
Due to genetic and reproductive differences, the offspring can only be created through in vitro fertilization of a human female egg/male “alien DNA.” Notably, only female humans can carry the child. The procedure, still new and risky, holds a 72% chance of failure. With the cost for the procedure almost triple that of human-human in vitro, only very wealthy or very devoted inter-species couples consider it.
The controversy surrounding alien/human crossbreeding stems from the fact offspring of such pairings are born sterile. However,reconstructive DNA processes can create a genetic coding altered to be “human” or “alien;” this allows their DNA to reproduce with an alien or human to create a child who is actual a mix of both. Moral and ethic debaters of both species have argued this mixed DNA will allow future aliens to adapt faster to land-born environments and vice versus for humans, while others believe this ventures into the dangerous implications of “playing God in science” with sentient beings.