Humans like to create classifications for things. It's one of the ways we try to understand the world around us.
Some classification systems are based on very simplistic two options. The "left hand" and "right hand" classification is one example of this. And like any limited classification system it might look nice and tidy but breaks down when you try to impose it on real life which is rarely ever so nice and tidy.
And what do we mean by "right hand" and "left hand" anyways? Do we mean "right hand" equals "good", "helpful", and "left hand" equals "bad", "harmful"?
Take a healing for example. For the patient that is suffering, being healed would definitely be considered "good". But look at it from the point of view of the microorganisms (bacteria, virus, whatever) that is causing the illness -- to them having the patient healed usually means killing the microorganisms. So to the microorganisms the healing would definitely be "bad".
Or look at a specific tool such as a knife. The knife could be used to cut food, to carve a piece of wood into a useful item. That's "good", right? But that same knife could be used to injure a living being, perhaps even to kill them. That's "bad", right? So is the knife "good" or "bad"? (Can a knife be "good" or "bad"?)
Magic is a tool, just like a knife. You can use magic for "good", and you can use magic for "bad". Specific spells can also be used for both "good" and "bad" -- it all depends on your perspective, and what your goals are.
It's no different when you use the labels "right hand" and "left hand" for a practice, a spirituality, or for spells and magic.