Was there anybody else on the show who, once he or she got to be a vampire, didn't want to be? Angelique didn't want to be, but it wasn't because of any ethical issues; she just didn't want to be tied down to the craving. She found lots of other fine ways to hurt people when she wasn't a vampire. Tom Jennings, originally a nice, ordinary guy (I believe Joe mentioned that Maggie dated him way back when), embraced being a vampire with unbridled enthusiasm. And so on. Becoming a Dark Shadows vampire causes radical personality changes, and some of them may not be entirely reversible even when the subject is cured.
I haven't seen all the Dark Shadows vampires, but I never hear about one, other than Barnabas, who wanted out, and I do remember the specific offer being made to one of them, who turned it down. It must have taken extraordinary strength of character for Barnabas to want to be human again. What would have happened to Julia if the vampire whom she lured to her bedroom had been anybody other than Barnabas? Golly, she didn't even have a cross in her pocket just in case!