"Is there some standard defense besides 'don't be somebody people want to mind-control'?"

"You can fight it off with practice. The problem is that arrangements to practice are hard to come by because of the 'life sentence for casting it on another person' thing."

"Seems like a coordination failure."

"Little bit. To be fair, right now there are considered no legitimate reasons to learn it, if 'practice' were a legitimate reason to learn it then lots more people would know it."

"...it takes a substantial time investment to pick up a spell and you learn to turn kittens into dishes?"

"Transfiguration is the practice of turning things into other things without, say, a particular kittens-to-dishes spell; if you master the principles which kittens-to-dishes is good practice at, then you can do arbitrary transfigurations. Charms and curses you mostly learn a spell and practice that spell."

"Which takes how long?"

"Depends on the spell, but days to months, typically."

"Okay then."

"Much longer than that to rederive them just from knowing they exist, so controls on knowledge of the Imperius probably makes sense."

"Where would one pick it up?"

"Personal instruction from someone else who knows it, usually."

"So all I need to worry about are evil intellectual dynasties which like collecting powerful magic, grand."

"Most people go through their whole lives without ever getting Imperiused, but it seems like it's worth being paranoid."

"I am not most people."

"That too."

"We could still make lots of progress if I never actually ventured into your world."

"Might in fact be the safest way, yep."

"Maybe I could terraform your Mars. I always wanted to terraform Mars."

"Um?"

"I guess it's not the most efficient use of my time."

"I just haven't the faintest idea what terraforming is."

"Putting air and water and plants and stuff down on it."

"Oooooh. I take it there's also a means to get there with Muggle technology -"

"Yeah, sure. Takes a few days, it's far away."