While this is true (that diplomatic immunity poses problems with some diplomats heavily abusing it, while there doesn't seem to be a good way to punish them for it), it at least is a phenomenon that can be seen as a cost to bear for a greater good: protecting representatives of other countries from becoming targets of a sort of "state-organized bullying" by the officials in power, which often makes it possible for these representatives to enter foreign states in the first place and which thus can be seen as a mutual agreement that fosters peaceful diplomatic exchange between countries.

For these weird PBA cards, I can't see any positive effect for society as a whole that could be brought up in their defense. This is clearly a form of institutionalized corruption, pressed into a handy credit-card format, and it is unworthy of a country like the United States.