The subject of the experiment did it willingly, but the Solomon family is also described as being obscenely wealthy so it's conceivable that they would have had the money to make any potential legal issues from the widow or the doctor... "go away".
So the bad guy's evil master plan was to kill himself? It seems like if everyone had just given him what he wanted, all their problems would have taken care of themselves.
Actually, the reason why the Big Bad was Bad is because he wanted to push the world into another dark age by killing Katherine and destroying the products of Noetic Science.
I'm still wondering what he himself would gained had he succeeded. While he may have rejoiced in jump-starting a new dark age, as stated above, wouldn't he have wanted to stick around to enjoy it? Sure he believed he'd be reborn a demon-king but it is hard to see what practical gain that would be. Of course he may have thought he'd also get a physical resurrection if he did it properly, but there's no way to really be sure.
Most likely he knew the real damage would come from that a.) his father would have lost his entire family, including his own son slain by his own hands, and b.) the Masonic ritual video of the government officials being broadcast to the world, causing outrage and panic. Still it's one heck of a step to take to get even.