Well, first of all, I think you may want to do a little background checking on the beings you're evoking. Every type of being has both benevolent and malevolent souls. Daemons, fae, gods, humans, dogs you name it.
Perhaps your assumptions that daemons are all malevolent and can be casted away with holy water is causing you to attract malevolent ones?
Just because you're a black magick user doesn't mean you have to work with "evil" or perform "evil", that is actually a misinterpretation of the craft made by outsiders, usually Judeo-Christians. Black magick is merely embracing the dark goddess or "crone" aspect of the goddess, living up to "Do as thou will, that is the whole of the law" or focusing on the darker side of life (ie: death).