Altruism is a funny thing. Having not yet read Ms. MacFarquhar's book, nor any other devoted to the topic, I can only say that altruism sometimes reminds me of people who spend too much time primping and admiring themselves in the mirror. Being  concerned with the well-being of one's friends and family is one thing: a human obligation towards those whose existence is central to our own identity and sense of what it means to be human. Being concerned, or overly concerned, with the well-being of strangers would appear to be dangerously aberrant; possibly turning toward self-destructive. Unless you are a pope---that station is an especially rare form of madness. Now, I suppose there are certain perks attending rampant altruism. Some folks are given recognition, and yes, even money when they espouse and pursue philanthropy. Often, philanthropists are held in the highest esteem, and of course, this makes them feel pretty good about their cause(s) and themselves. And so the relationship between altruism and philanthropy seems a close one.
We do enjoy feeling good about who we are and what we do. Pleasure vs pain. Self-esteem can be a natural state of being, or it may be artificially acquired  through "selfless acts of altruism". In either case, the motivation is most nearly selfish at its base.
Neuman

It seems like most of the discussion here was of altruists who took a different path to happiness not those who sacrificed happiness for altruistic reasons.  Am I missing the point?  Let me comeback to this.  I will read this book and check back here.
The soldier  or Mother Teresa are in a different category than couples making a quarter million a year and living below their means.  I have to think about this.  Not sure if this show is misguided or if I am.  I think it might be both.

Rawls's notion of the maximin comes to mind, obviating the question by maximizing the well-being of all. I find obsessives highly annoying (activists, religionists and the like). It is hard to see how the rich of today can live up to their means anyway, it is no more impressive that they spend it on philanthropy than on a lavish lifestyle. But the lower-class obsessives would be unnecessary if the resources available were distributed fairly. But fanaticism is inauthentic in any context.

In the vein of good feelings, my recent essay on the notion of infinity might give some insight. I will share some excerpts, if I may: I said that people feel better about things they can qualify or quantify, The evolution and continuing sophistication of human consciousness gives rise to an expanding need for comfort in this regard, hence, the growing emphasis on qualitative and quantitative measures from amoebas to zygotes...A little later in the piece, I said I had no quarrel with any of that. But, unless you love the heat of philosophy, the thrill of agony and the victory of defeat, you may as well cross infinity off your list, be that 'bucket' or otherwise. It is not an achievement. Nor a destination. Neither you nor I nor anyone else will ever get there...there is no 'there' to get to....Well these are only small snippets of a rather short writing. The key notion here is the comfort factor and our NEED-TO-KNOW, even when there is nothing to do with that knowledge. A little different from my 2016 observations---but, I have had some time to adjust, and that has made ME feel better...