The 2yo and the light switch is not quite a loophole – it is much “iffier” than that. But if he doesn’t know better than it can be considered something of a “loophole” (and I plead guilty).
By Mesiras Nefesh do you mean Sakanas Nifashos? A life-and-death situation? Shabbos is not one of the “yeihaig v’al ya’avor”s. Some people translate “sakana” rather loosely sometimes: a broken arm on shabbos afternon is NOT a sakana, but a possible heart attach IS.
There are many mitzvos where people look for the loopholes and the shortcuts. (Do I even need to say the word tznius?) Doesn’t mean that we should.