No, there should not be a legal duty to help another person who is in trouble. The reason for this is that it would be extremely difficult to write a law that would be understandable and would include good rules for when the duty applies and when it does not. Laws need to be understandable so that people can know whether their actions are legal. In this case, it would be very hard to make the law understandable and good.
Clearly, we would not want to obligate people to help others at tremendous risk to themselves. If I saw a child about to drown in surf that was so high that I was sure it would kill me, should I be obligated to help? Surely not. The problem is that it would be very hard to quantify how much danger a person would have to put themselves in when following the law.
Clearly, we do not want to legally obligate people to help anyone who is in any kind of trouble. For example, if I see someone who has a flat tire at the side of the road in broad daylight, am I obliged to help? How much trouble would they need to be in before I had to help? This, too, would be hard to quantify.
If we tried to put such a law in place it would be very difficult because people would not know how much danger they had to put themselves in and they would not know what constituted a person “in trouble.”