My dear boy,
There are those who would tell you that the Dark Arts are dangerous and addictive, feeding off all that is malevolent in the human psyche. There is some element of truth to this, but it obscures the more profound truth – it is not the Dark Arts themselves that are seductive but the power that they bring, and it is that power which tempts people into casual cruelty.
The bourgeois morality espoused by the Ministry doesn't prevent them from using the same Arts, it merely allows them to restrict their use to those they approve of, and allows the average Witch and Wizard to stand idly by whilst brutality is practiced in their name.
I have been a loving husband and I hope that you will consider that I have been a good father. But according to received opinion – one hardly dare call it wisdom – I should be so much the slave of the Dark Arts that I should be hip deep in blood and buggering the House Elves twice a day. I rather think your mother would object to both practices. There are actions that I have taken – distasteful actions that some would consider beyond the pale – but they have been out of necessity and not for enjoyment.
I drink wine; that does not make me an alcoholic. I eat food; that does not make me a glutton. Why, therefore should using the Dark Arts make me their servant and not their master.
You practice them because they are useful, and for what they can bring you. You practice them to obtain power and influence, and you do that in the full awareness that it is the power and influence that are seductive and not the magic.
The Arts are a window into the soul. Most people are good, not because they are inherently good, but because they are afraid to be bad. They do not have the power to enforce their wishes, so they speak with horror of these matters so that they can conveniently pretend to themselves that they are not like that, that they would never kill or inflict pain on another, and gloss over the thousand trivial cruelties that they visit on others daily. Not for them the hot rush of Crucio or Avada Kedavra; instead it is the death of a thousand cuts of sneers, resentment, bullying and bureaucracy.
But if they were given their way, just for one night, what monstrous things they would do: what rapes, what murders, what tortures they would inflict on those who had crossed cross them.
It is these little men that are the most dangerous. They are powerless in their insignificant lives, and can only take their revenge in small ways, and dream bloody dreams of revenge and domination. Pettigrew was one such man. He did not betray his friends for the siren call of the Dark Arts, but for jealousy, for pride, and in the futile hope of gaining the respect and admiration he had been denied elsewhere.
That is not the Malfoy way. We do not need to seek out respect and admiration; our position is assured. There is little that we could not already achieve by the use of money, power and position. What power can the Dark Arts have over us then? Therefore, we may use these Arts that other, frailer, men are afraid to use. You should not rush to use these tools, but neither should you shy away from them; they are there to be used prudently.
I only wish that it were possible for me to provide more detailed and practical guidance on the matter.
Until that time comes, I remain,
Your loving father,