As pointed out on the Headscratchers page, the problems between the Jets and Sharks probably would have calmed down eventually if the cops were around more. Not because the cops themselves would have stopped them; because of both groups' shared disdain for them (and, at least in the case of the Jets, their disgust at the cops' assuming their motivation is racism).
One of the ways the Jets and the Sharks are not so different is that, while the Puerto Rican Sharks are natural-born American citizens, they're mistaken for any other Hispanic immigrant; and pretty much all of the Jets have Irish, Italian, and Polish ancestors, all of whom were stigmatized at the time.note The Irish were portrayed as drunken hooligans prone to violence. With World War II still being fresh in people's minds, some of the Italian-descended Jets may have grown up being regarded as outsiders because Italy fought on the Axis side. And the Poles have historically been painted as job stealers, and the latter half of the 19th century saw tension towards Polish immigrants rising because of their Catholic faith. All three groups were regarded as "ethnic whites" because they were neither Anglo-Saxon nor Protestant.
In this way, back in 1957 they would have seemed closer to Romeo and Juliet's "two households both alike in dignity": two disenfranchised immigrant groups, fighting each other because they can't fight the system that oppresses them both. It's only in more recent decades, when the concept of "ethnic whites" has mostly died out, that the "both sides are to blame" portrayal of their feud has gained a sense of Values Dissonance, because the Jets now come across as more privileged compared to the Sharks than they really would have been in their time.
