I would imagine that your situation being a crime isn't very possible
1) You and the sinking man are alone, and therefore no one is there to report you
2) There are other people who wish to save him, so they call. No harm no foul.
3) There are other people who don't wish to save him, in which case they also commit the crime, and are equally guilty.
It would be like making blowing up planets illegal. Sure, it's a bad thing, but it's so completely unlikely to happen that it's not worth the documentation it would take to make it a law.
1) You and the sinking man are alone, and therefore no one is there to report you
2) There are other people who wish to save him, so they call. No harm no foul.
3) There are other people who don't wish to save him, in which case they also commit the crime, and are equally guilty.
It would be like making blowing up planets illegal. Sure, it's a bad thing, but it's so completely unlikely to happen that it's not worth the documentation it would take to make it a law.