Organ donation is, of course, an important way of keeping people alive. People surely should sign organ donor cards because, once you are dead, you have no need of your organs and they ought to go to someone else if they could be useful.
I do not know if our system of getting organ donors is a good one, though. I wonder if the government should be more aggressive about trying to recruit donors. I wonder if we could have an "opt out" system instead of an "opt in" one. In other words, I wonder if people would accept a system where everyone's organs would be taken unless they specifically say they don't want that.
Organ transplant is not an option that some people choose to exercise. There are a large number who have their organs damaged due to diseases or in accidents. It is essential for them to receive a healthy organ to survive.
Though research is going on to find alternate ways to treat illnesses that presently require organ transplants, we are long way from eliminating the requirement for people to donate to their healthy organs.
Once a person dies, s/he should donate her/his organs. As it is essential for people in the US to consent while they are alive to having their organs taken for transplantation into others after they die, everyone should sign their organ donation cards. There cannot be a better way of leaving this world than with a gift of life given to someone else.