I cannot accuse the American political philosopher Michael Sandel of setting up a straw man in his criticism of cosmopolitanism (Democracy's Discontent, new edition 2022), which historically has been presented to us an ideal for humanity. Sandel himself cites Kant and Marx, but there is a much older thread, especially in Christianity. If that ideal were to be taken - which it usually is not - to mean that we have no special friends or relations and must treat all strangers equally to anyone we know personally, then Sandel is right that it would be unrealistic and even inhuman. But that is far away from how universal concerns, which can lead us in a cosmopolitan direction, now present themselves. In the 21st century world they appear much more often as menacing threats that might destroy us than as a romantic picture of peace and love.
The current wars - at least two of which threaten to expand with the nuclear dimension lurking in the background - illustrate a more general point about particulars which Sandel (rightly) says we attached to. In many cases particularities will fail to recognise their own particularity. This is most obvious with religious extremists, but is also common amongst economic interests and lobbyists. A warning sign is apologists who claim to speak for the 'people'.
Running alongside this problem is the age old hazard with particular concerns and friendship or family loyalty of sliding into depravity through corruption, cronyism, and abuse of power. Universal ethical values were invented in part to combat that danger.
None of this means we can, or should, abandon our personal and particular concerns. But in the dangerous and very unequal world of the 21st century we have to recognise that universal dangers have the power to crush our particularities if they are ignored. A sensible ethical approach might be similar to Charles Taylor's 'politics of recognition' scheme for a constitution guaranteeing certain basic universal rights but leaving others to discretion of particular communities (such as Quebec in Taylor's plan). In any event, it makes sense for us to think of universal concerns, and then cosmopolitanism, not as a dreamy ideal but as response to danger signs.