Luther Gulick, the elder namesake of Luther Gulick Playground and Park, was a tireless advocate for urban green spaces and, above all, play spaces. In the days before extensive urban planning, and certainly before a widespread appreciation for smaller local parks, Gulick argued for just these. He argued that providing play space for children was essential to their growing up healthy and even moral—offering children positive outlets for their time and energy. Below is his obituary from the New York Times, followed by a letter he wrote to the Times and brief article on a lecture he gave. They provide a good sense of his advocacy.
In the lecture from 1905, Gulick argues that only a 20-story waterfront pier of playgrounds could feasibly provide enough public, open space for children of the Lower East Side. A 20-story glass-enclosed play space would be a bold proposal today, let alone in 1905!
In the letter to the editor, Gulick argues that children have a right to use the public space for playing and that the city government has a duty to provide safe spaces for children to be children in (and not to leave it up to the whims of charity).