If you could single-handedly legalize it, it would be a good idea, but you can't. You might be able to help, so that you add a tiny probability of success, or a tiny decrease in the time necessary. Since you're helping a lot of people, it makes a significant difference over all. If you're only worried about one person, it's not really worth doing.

In your personal example, multiply the amount you donated by the increase in probability in getting the insulin pump. The result is more than the total costs of the insulin pumps, but is it more than it costs for one?