In Consideration of Dark Magic
What is Dark Magic?It's set out pretty simply by... someone. I don't know if it's canon knowledge, but I've been on several sites that define "dark magic" as magic that was created solely to harm.
By that definition, the spells that are in our dark magic section would not all be dark. Many of them have non-harmful uses.
Can my character do dark magic?My personal opinion is that most characters can't do it, simply because most characters don't have access to that information. Not even all children of Death Eaters would have learnt those spells, because Death Eaters need to fly under the radar and a child who showed off something like that to his or her friends would incriminate their parents.
Can my character do the unforgivables?This is a completely different question, because the unforgivables require feeling to work. Bellatrix tells Harry "you have to mean it." Which, to me, means you have to want to hurt the person.
Basically, almost every witch and wizard knows the incantations of the unforgivables, but very few of them would be able to successfully cast them, because very few of those people would
truly want their victim to suffer.
So when Harry tries to curse Bellatrix, his curse splutters out because even though he's striking out at someone who he thinks he wants to hurt as much as he can, deep down inside, there's part of him that doesn't really want her to be harmed.
Most people are like Harry. I know I'm like Harry; I don't like seeing things like people who pull the wings off flies. Being able to say the curses would not mean your character could do them.
Of my twelve characters, four of them could potentially cast the unforgivables, and even then (ironically) Caelani & Lucius could only do it under certain circumstances.