I'm just thinking that it's not just death of demon vs. chance to live for the host, but that if hell is rather more like a revolving door than a semi-secure prison for demons, any exorcism means risking yet another innocent who will be the next future host. Clearly what they really need is better ghostbusting demon hunting equipment so that they'd have this kind of vacuum cleaner tool to suck the demon smoke in once its exorcised and then find a way to kill them eventually outside a host or something. Or store them like radioactive waste. Too bad Ash isn't around anymore, they could have used a techno-geek for research into that. I mean, the whole colt thing is very much stuck in the 19th century as far as equipment goes.