Not necessarily to contradict your point, but your analogy does not paint the picture that I interpreted from your second paragraph. Consider this;

I certainly would not want harm to befall my daughter, but like me, she still chose to be an organ donor. If the worst should happen, our loss might still bring a benefit to others. The pain aside, if she was killed in a say, a car accident, I would be fine allowing her organs to be taken to save someone else. As I'm sure the recipient might feel empathy for our loss, they would be happy to accept the life saving gift. Now say instead, they murdered her to take her organs to help the dying patient. Is it ok then?

Heartless as it may seem, this becomes a grey area. Because of course I'm opposed to the murder of my child, but I'm not opposed to organ donation. As I'm sure the recipient is happy to accept a donated organ, but a stolen via murder organ presents a dim light on it. Obviously if you are opposed to organ donors all together, this becomes a moot point; but if the act is just, then we are really talking about the circumstances involved.

Now I hope to never have to face this choice, but if the latter was true, would I still donate the organs? She is already dead, and any legal (or not) actions I take afterward will still not change that fact. So at what point is it a principle of ill gotten gains and as such ok to refuse the possibility to save someone's life? On the other hand knowing that in a way, I was supporting the "ends" of the horrid means, might not be a point I would be acceptable with. I'm sure the recipient might have to choose the line they are willing to live with as well.

I guess the point I'm trying to make is, that the issues does not hinge on a didactic set of options. There is of complexity of issues that are involved when considering the morality of ESC. Most people are not going to agree to murder people who are already living their lives (children or not), but the potential for life is the gray area. I'm sure the main contention is at the point of where life begins, as such, it becomes "killing a cell" to "murdering a baby." As a meat eater might be picky as to what types of meat they eat, and what is involved before it's given to them; to a vegetarian, there is only one choice.