I think that, while it's true that some people might do this, this seems like an especially steep price to pay if it's the only benefit afforded to us by rationalization. (I realize you're not necessarily claiming that here, just pointing out that rationalization seems to have some possible social benefits for a certain group of people.)
If we are crunching the numbers, though, it seems like the flip side is much much more common, i.e. people doing things to benefit themselves under ostensibly altruistic motivations.
"If we are crunching the numbers, though, it seems like the flip side is much much more common, i.e. people doing things to benefit themselves under ostensibly altruistic motivations. "
Well, this is typical behavior, we all know that.
That is why I was puzzled by the phenomenon when everything happens in reverse.
But a much more common situation is when people clearly indicate and voice their position: they enter into interaction with others for the mutual formal benefit of both parties (nothing personal, it's just business), or for altruistic reasons.
But what my observation reveals, and what is probably even more common, is that people interact very often simultaneously satisfying both needs - for the good of others (you can call it altruism) and for their own good
If we talk about rationality in the broad sense of the word, as it is used on lesswrong, and not about rationalization in the narrow sense (and in general, these are different words with different meanings, although one-rooted), then rationality means "how a person should think and act in order to maximize the benefit of all, and the concept of "all" includes all people equally, and therefore himself"
Usually, people talk about rationalization ("the act, process, or result of rationalizing : a way of describing, interpreting, or explaining something (such as bad behavior) that makes it seem proper, more attractive, etc" https://www.merriam-webster.com/dictionary/rationalization) in a negative context: a person does something bad, or at least does it out of reprehensible motivations, but then rationalizes his act, bringing worthy motives under it.
But recently I have come across the rationalization of good behavior, through selfish motives. In other words, a person is not free to do good things, and they need a selfish motivation to look practical in their own eyes. For example, a person donates clothes and other things to an orphanage and says that they do it for their own sake, because they have a system of biological encouragement for socially positive actions. But he innocently forgets that it was not in his will that such a system of unconditional encouragement was laid down in him by evolution. Or a person becomes a vegetarian, not for ethical reasons, but because it is "good for their personal health".
That is, some inherently good people are so dependent on a certain layer of culture that forbids them to do altruistic actions of their own free will that they are forced to rationalize good actions by saying that these actions are in some way beneficial to them personally.