I have to agree with Marael on this, it seems many have missed the sheer basics of magick or energy in general.
If you have read the 7 laws of the universe or have taken up anything on the subject of magick or Alchemy throughout history, you'd know that black and white are simply a case of polarity.
There is no such thing as good/evil. Only right and wrong (2+2 = 5 is not evil, but it is wrong), and these are subjectively dependent on your intentions, also known as true will.
In this case, dark magick is the magnetic force that pulls, and stands for individuality, freedom, chaos, too much of it results in destruction and disruption, but the lack of it could lead to a overprotective, benevolent dictatorship like situation with a lack of individual freedom or even life.
Light magick is the penetrative force that stands for control and the benefit of the many, too much of it leads to things previously mentioned, but a lack of it leads to chaos and disruption.
In short, too much of either light or dark energies is wrong for us as humans, it will fuck our shit up. Neither of these energies is good or evil. Without dark energy there wouldn't exist any gravity and, well, I am sure we can all imagine how that would be bad for us on the physical plane of existence. Only an extremely polarized person would claim that 'dark' equals evil or bad, or necessarily harmful. And to think that 'white' magick cannot be harmful has never been actually afflicted by light magick.
Also, white magick also uses dark energies as well as light energies. And Black magick also uses light energies as well as dark energies.
White magick is for influencing and adapting yourself. Black magic is for influencing and adapting your environment. Their names however do not originate from their intention, but rather from where they are known/thought to have originated. Black Magick is thought to have originated in Egypt, which was back then known as 'The Black Lands', so 'Magick of the Black Lands' or Black Magick for short. White Magick is thought to have originated in the snowy mountains, you guess where....but you probably already guessed the place was known as 'White Lands' and 'Magick of the White Lands' has then come to be known as 'White Magick'.

So in short: a hammer is a hammer. But a hammer can be scary to one who thinks it's a murder weapon, while the other thinks "hey, a hammer, I could use that to build a tree house". All decided by the intention of the individual. but does that mean we need to ban all hammers because one used it to bash someone's head in?

being polarized is all right, mainly using one force to guide you in magick also is. but before you even start using either consciously, you should know their clockworks outside of any specific movements or religions that teach magick.