I would not agree with anyone who believes that you need black magic to protect your self.
As 2396022 said, it is like fighting fire with fire. White magic is used for protection mainly, as well as healing and personal gain without harming anyone against their will.
Black magic is used mainly to cause what white magic does not, brake of free will, harm and negative energies.
With a few words, your karma will be suffering.
However, there is a difference between knowing and practising. I for example have no problem reading black magic (Although I do not usually do) but I would never practise it on somebody as I am practising white magic.
And remember, magic has no categories.