Suppose some rich people actually got rich by dishonesty, exploitation and selfishness. Believing that rich people get rich because they deserve it will then mean either (1) believing that dishonesty, exploitation and selfishness are good or (2) believing a bunch of falsehoods about how those rich people got rich.
#1 is clearly harmful, to the individuals involved and to society as a whole. #2 is probably also harmful, not so much because it matters what everyone thinks about how particular rich people got that way as because believing those falsehoods probably means believing a bunch of other falsehoods about, e.g., how business and society actually work, and it's probably bad if everyone believes a lot of false things about that.
Suppose some rich people actually got rich mostly by good luck. Believing that rich people get rich because they deserve it will then mean overlooking the importance of luck, and believing that people who don't get rich deserve not to be, and probably to believing that people who are poor deserve to be poor.
That's harmful because it begets a lack of sympathy towards others in need.
There are no doubt positive effects too; e.g., if you think that hard work reliably makes people rich then you may be more likely to work hard, and maybe it's good for society if everyone is willing to work hard. (Though I have my doubts about how well that sort of self-deception can actually be expected to work.) But it's not at all obvious, at least to me, that the overall effects are good, because of harms like the ones I described above.
(... Maybe you were being sarcastic, in which case I apologize for missing your point. But it looks to me as if you meant what you wrote.)