[This growth may be attributed] to several factors, including the rise of the women's movement, which was attracted to the notion that the divine includes feminine forms, and to environmentalism, which is prompting the search for religious expressions that see spirituality as being a part of nature rather than above it.
But about those Earth Day celebrations... If you're working for the city, you shouldn't be staging religious rituals. That's basic Establishment Clause law. But even if you're not working for the government, it's still not right to trick people into performing religious rituals. But some religions are treated as if they are just a sort of playful folklore. A little Paganism for Earth Day, a little exercise in Hinduism or Native American religion for the kids.
Is that a problem?
Maybe not. Most of us play around with religion on Halloween. Don't we often engage with the folkloric aspects of religions we don't believe in? Or maybe we engage in folkloric aspects of our own religion that we don't believe in. I suppose it is a matter for each individual to decides how purely religious or nonreligious he wants to be.