As I see it, it's just a tool to try an unravel principles. They aren't trying to solve specific situations. Thought experiments often have counter thought experiments, like with the trolley problem, if pulling the lever seems more ethical, when you have 4 patients who will die without an organ transplant, and you have 1 patient who is healthy and organs could be harvested to save 4. It starts becoming harder to work out what the critical principles are. Just like in the article of the killing vs letting die, the assassin example is an alternative thought experiment. This is more important if you have to encode these things in laws / policy where you need a more generic guide to what is acceptable. But you wouldn't rely just on thought experiments to do this, they are just tools to help shake the "thought tree" to see what falls out.