There’s a difference between being willing to do that and being born for the purpose of doing that. The reality of “the heir and the spare” is that the spare exists only as “just in case”. And then once the heir has an heir the spare’s job is now to expand the family to help the heir line to remain “pure”.
I don't know them (obviously) but I doubt the Royal Family is that cruel to tell Harry that. No doubt they joke about it, like any other family.
My brother had thick, curly dark chestnut hair, while the rest of us had straight, ginger hair. We always teased him "he was actually the son of the milkman." (we didn't let mom hear that)
harry is just whiny