What enabled the government's shift in environmental policy and tha passage of meanigful environmental legislation in the 1960's?
Few can understate the importance and power of Carson's work. Bringing the harmful use of pesticides to forefront of the public, Carson began the process of asking how industrial growth can be balanced with the protective needs of the environment. It is probably in this paradigm where Carson's impact is most felt. She never advocated that business needs to be dismantled or displaced. Rather she stressed that, like all human endeavors, business is linked to a larger chain of connection and ecological awareness is of critical enough importance that it, by itself, can compel individuals to expand their scope of understanding to ensure that the need to make money does not come at the cost of other animals and our ecosystem. There is enough evidence to suggest this. At the same time, I would suggest that a collective increase in consciousness helped to spur on the issue of concern for the environment. The rise of the counter culture in the 1960s, and their particular reverence for the environment helped to instill an awareness of the need to understand that ecological issues must be understood by society and acted upon by Congress. The combination of both Carson's scientific calls for change through her work and the social consciousness that started to emerge in the time period could account for the passage of meaningful environmental legislation in the 1960s.
There are quite a few things that you could cite that allowed this to happen.
One of these would be the publication of "Silent Spring" by Rachel Carson in 1962. This book helped to galvanize opinion on the subject of pesticides and the environment in general.
I would argue that rising prosperity helped to allow this to happen as well. As Americans got richer, they were able to think more about things other than "pocketbook issues."
Finally, I would say the general anti-business, anti-establishment ethos of the '60s helped to push government towards environmental reform.
A great book that is indirectly related, but important to the discussion of environmentalism is Nuclear Rites. This book chronicles the the rise of nuclear power plants and weapons in America as well as those who have opposed them. The connection to environmentalism is that educated people began to get involved and opposed nuclear development and more importantly started to stand for the environment. When this class of people began to get involved, there was greater success. Before this, there was little success, because environmental issues did not seem important.