Plenty of specific crimes, do, in fact, have seeking a material reward/exchange as a required element of the offense, and the act that is criminal when done for profit is legal (or, if still illegal, illegal under a different provision which often has a lesser punishment) when done without that exchange.

I don't think anyone is suggesting that. But, at least in US law, there is a major distinction between commercial and non-commercial copyright infringement. Both are illegal, of course, but they are treated very differently.

That's decidedly not true.

Per your example:

> Otherwise the only murderers in jail would be professional assassins.

The people responsible for dropping the nuclear bomb on Hiroshima were not considered criminals and did not go to jail or get punished at all.

War acts are always rationalized by their consequences and the intent behind them.

But this is way off-topic.

Someone already mentioned that copyright laws do indeed distinguish between "commercial and non-commercial copyright infringement".

Actually, I'd argue that even ethically they are treated differently.

If I bought a movie then shared it with my friends, no one would think I'm doing something that's unethical.

If I started selling or renting that movie to my classmates, it's more controversial.

Man, wouldn't that be a better world? But in the world we live in right now, lots and lots of actions are illegal for profit and legal otherwise.