Every year I’ve lived in New York City, a day unexpectedly arrives — usually in May or June — when I step outside, take a deep and appreciative breath, and realize that for the past several months, I’ve been suffering from mild seasonal affective disorder. Basking in warm sunlight again, I watch the rest of the city come back to life. I get a particular buzz walking by or through the city’s parks, our collective sites of celebration for the return of warmth, where music blasts from boom boxes and portable speakers, and the whiff of the masses grilling and chilling is heavy in the air.

It’s easy to take the city’s parks for granted. But when more and more social interaction takes place from behind computer and phone screens; when fewer and fewer people meet their romantic partners through real-world social networks; when fewer Americans report having close friends than ever and more say they’re spending less time with those they do have and feeling increasingly lonely — the very existence of public spaces for leisure, open for all to enjoy free of charge, is something to cherish.

Those spaces haven’t always existed. In the United States and elsewhere, public parks, recreation centers, and swimming pools were the product of social turmoil and political struggle, with socialists often playing key roles in creating and defending such spaces. Nobody’s thinking about class struggle as they flip hotdogs on the public grill. But because they serve the collective good rather than private profits, public parks are a challenge to the logic of capitalism.