system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] Why is Imperio an unforgivable curse but Memory Charms are standard practice?

It seems like altering memories is almost if not just as bad as controlling someone. You could do all sorts of things to a person by convincing them they'd already agreed to it.
gpt
The unforgivable curses are unforgivable not simply because of what they do, but also what is required in order to do them. 

From OoTP:
“Never used an Unforgivable Curse before, have you, boy?” she yelled. She had abandoned her baby voice now. “You need to mean them, Potter! You need to really want to cause pain — to enjoy it — righteous anger won’t hurt me for long — I’ll show you how it is done, shall I? I’ll give you a lesson —” - Bellatrix.

The killing curse works because the person casting it wants to kill, wants to commit murder.

The cruciatus curse works because the caster wants to cause pain. They revel in it. They want their victim to feel pure agony to the point where they would rather die than endure another second of it.

The imperius curse works in the same vein. The caster enjoys the total dominance that comes with it. A well cast imperius curse is incredibly difficult to break by anyone. In the instances where Harry does break free of it, he knows it's coming or is on high alert already. 

To sum up, it's not so much the effect of the spell that is unforgivable, but the addition of the mindset required in order to properly cast them that earns you a life sentence in Azkaban.