Surely, if there was a completely legal way to inflict great harm on humanity for only $1Million then there are a ton of people/groups with the desire and resources to do those things.

Are you sure? Who? The people who do inflict great harm on humanity aren't cartoon monsters. They're commonly either unethically selfish, foolishly utopian, or terroristic. The selfish ones will only care about an idea for doing harm if the harm is a byproduct of an idea for getting something they want. The utopians don't try to do harm, they just create unintended consequences when trying to do good. Neither kind of person is going to be at all interested in an idea whose sole purpose is to do great harm.

Even terrorism is typically either a negotiating point for demands, a provocation to overreaction, or at worst a pure act of revenge; here they actually have a desire to do harm, but targeted harm, not generic "harm on humanity". Unless an efficient act of anti-altruism happens to affect only a subset of humanity that's contained within a set of terrorist targets, it's not even going to interest them!