There are three Unforgivable Curses:
- The Killing Curse (Avada Kedavra): Kills someone
- The Cruciatus Curse (Crucio): Causes pain
- The Imperius Curse (Imperio): Controls their will
But what about the Memory Charm (Obliviate)? Despite its label as a charm, shouldn't it be classified as an Unforgivable Curse?
We see them quite clearly in Chamber of Secrets where by Lockhart's own admission, it has the power to make someone lose their minds:
'The adventure ends here, boys!' he said. 'I shall take a bit of this skin back up to the school, tell them I was too late to save the girl, and that you two tragically lost your minds at the sight of her mangled body. Say goodbye to your memories!'
He raised Ron's Spellotaped wand high over his head and yelled, 'Obliviate!'
Harry Potter and the Chamber of Secrets - p.224 - Bloomsbury - Chapter 17, The Chamber of Secrets
As Au101 wrote in this answer about why Gilderoy Lockhart couldn't recover from his backfired Memory Charm:
"'Say goodbye to your memories!'" There's no talk of wiping out the last 24 hours or anything like that. "[Y]ou two tragically lost your minds", he's not just gonna do enough to get away with it.
Wiping someone's mind permanently seems like a short step away from outright killing them. And even if they don't completely wipe their mind, it seems like a huge personal violation to tamper with another person's memories. You could make them forget something really precious to them (e.g. the day they met their spouse) or some harm that was done to them (e.g. abuse).
Given all of this, why isn't the Memory Charm (Obliviate) an Unforgivable Curse? Or for that matter, why isn't it regulated at all?