[genefromjersey]

I think it became a perjorative gradually: Royal bastards were often a problem in matters of succession. (Queen Elizabeth 1st had been declared a "bastard" after her mother was beheaded. It was complicated: don't ask ! )

The Noblemen of France and England were apt to be quite democratic about sowing their "seed", and there were often revolutions based on dissatisfied barons pledging loyalty to one royal bastard or another.

Incidentally, one of my children ( I forget which one ) was legally a "bastard" until adoption. Perhaps this explains why I am a bit sensitive about the term...

[Pearls Before Swine]

Royal bastards were often a problem in matters of succession.

True, true. Maybe the bad rap on bastardry developed historically as a top-down problem rather than a bottoms-up problem.