> When the deceased was committing a felony themselves, why can't they take 100% of their own felony murder charge? We don't need multiple people to face full consequences for a single act.

If you view punishment retributively, as a blood price that must be paid, that argument makes sense -- when you have multiple people available to take the cost, only one of them should need to (of course, if you view it that way, its hard to see how the person who died can, if felony murder has a blood price, be said to pay it.)

But, while retribution is no doubt part of the basis of punishments in the American system, its not the sole basis. If two people act together to commit a murder directly, we punish them both as principles. If two people act together to commit a felony in which someone is one of them -- whether or not it is one of them -- why shouldn't both be fully liable (whehter or not both can be punished) for felony murder?

A crime doesn't necessarily have only one principal, and when it has more than one, we don't generally only punish one. And if it has multiple principals and one of them is not subject to the jurisdiction of the court, or immune to punishment for some other reason, that doesn't absolve the other principals of punishment. I don't see why felony murder, presuming that we should have it at all, should be an exception to that rule.

The law may work this way, but our social notions of justice do not. Talk to ten people on the street about the circumstances of this crime ("A and B rob a bank; B gets shot and killed"). Ask them how they feel about these two statements:

1) "It's A's fault that B got killed"

2) "It's B's fault he got himself killed"

I doubt you will get much agreement with #1 (I would expect responses like "did A talk B into it?") and I'm pretty sure you will get lots of agreement with #2. The law (effectively #1) is incongruous with our prevailing notions of morality and responsibility.