The guy who came up with Black Rose is an elezen, but he was fully cooperating with the Garleans the entire time. Furthermore, he hid a few containers of Black Rose in the Fringe and gave himself amnesia as one last "Fuck you!" to Giaus after Giaus shut down his his pet project. Giaus is recorded as being very annoyed that the XIVth Legion would never find all the manufactured Black Rose since killing off the population whole-sale was never his goal. From all accounts, when the scientist was in his right mind he didn't have a problem with what he was doing, if anything he enjoyed it too much...