A member of the studio audience as asked me to address the question
Why would it ever be rational to put someone else's (overall/net) well-being ahead of your own?
This is not an easy question to answer, in part because some of the terms are not clearly defied. Specifically, what is meant by "rational" or "well-being".
We could simply define "rational" as that which promotes the well-being of the agent. In this case, it would never be rational for an agent to sacrifice his well-being for another. On the other hand, we could simply define "rational" as "that which maximizes the total number of paperclips". In this case, it would never be rational to do anything that does not maximize the total number of paperclips.
However, these types of maneuvers would invite a new question: "Why should I actually do that which is rational?" Questions about rationality ultimately seem to be questions about what to do. If we preserve this connection, then we have to limit our discussion about what is rational to things that people have a reason to do. If there is no reason to maximize the total number of paperclips, then there is no definition of rationality that makes it rational.
So, we link rationality to what there are reasons to do.
The other term to look at is "well-being".
The trick here is that the term itself is a value-laden term. "well-being" means, "a state of being that is good" or, more relevantly, "a state of being that an agent has reason to realize".
We cannot even answer the question, "Is an agent better off?" without first determining what states the agent has the most reason to bring about. A state of being is not "well-being" without being a state that the agent has a reason to bring about.
Now, we could define rationality in terms of that which promotes a state of being that the agent has the most and strongest reasons to support. In this case, it would still be true that what is rational is that which promotes an agent's well-being.
However, this still invites the question, "Why give one's own state of being a priority over all other states one might have reason to promote - such as the state of somebody else's being?" Can one identify, in the real world, an "ought-to-be-consideredness" that resides solely in the state of one's own being, and in nothing else that exists? In other words, is it the case that concern with other states cannot exist, or can exist but should not?
There is good reasons to hold that other concerns can exist and do exist - and without them the human race would not exist.
The main thesis of Richard Dawkins' The Selfish Gene is the idea that we are disposed to acquire those interests that tend to replicate our genes. These are sometimes incompatible with our own state of being.
Take the desire for sex, as an example - an interest in realizing a state of being in which "I am having sex". This is an interest that tends to promote genetic replication. However, it is often incompatible with the well-being of the agent. Sex consumes time, energy, and other resources (not only in the act of sex but in getting into a state where sex is even a possibility). It makes one vulnerable to otherwise avoidable diseases and other forms of harm. For females, it could result in pregnancy which puts a massive strain on the body - often leading to death. If it results in a live-birth, the self-interested thing to do would be to abandon the infant. However, mothers are disposed to have an interest in the child's well-being.
All of these are explainable in terms of interests molded by evolution - including other-regarding interests. However, they are not explainable in terms of interests only in one's own state of being.
So, other interests - other reasons for action - can exist, and do exist.
Perhaps they ought not to exist.
Here, I am going to offer a negative hypothesis - what reason is there for including some reasons for action and excluding others? What evidence is there for the existence of such an entity? Where, in the material world, do we find the "ought to be considered" within reasons relevant to one's own state of being but "ought not to be considered" within reasons relevant to the well-being of others?
I would hold that there is no reason to postulate such an entity - no evidence for this existence. While this does not imply that such an entity does not exist, the fact that there is no reason to postulate such an entity is as good as we can get - and good enough.
The member of the studio audience asking the original question postulated:
The only thing that I know exists is my own consciousness. I would argue that because of that, the only philosophical axiom that I can stand by is: What is 'good' for my consciousness is 'good'.
Without going into the question of whether one can know of the existence of other things, it does not follow from, "I know of the existence of X" to "What is 'good' for X is good".
If, for example, it were the case that the only thing that I know exists is torture, it would not follow that what is 'good' for torture is 'good'. There is nothing within the state of "I know of the existence of X" that implies "what is good for X is good".
Nor does it follow from "I do not know of the existence of X" that "There is no such thing as good for X". I might not know about the man who was inside a large tank cleaning it when I opened the valve to fill the tank with water. My lack of knowledge does not change the fact that opening the valve is not good for the man in the tank.
The questions of what we know and what is good are as different as the question about what we know and what is true.
Ultimately, I define rationality in terms of means and ends. Given a desire that P, it is rational to do X where X helps to realize P and not to X where X tends to prevent the realiziation of P. Given a set of desires, it is most rational to do that which realizes the most and strongest of those desires. Rationality, in this sense, comes in degrees. This applies to both self-regarding and other-regarding desires. There is no reason in the real world to assign "ought to be consideredness" only to self-regarding desires.