Sometimes the story of conservation reminds me of the joke about the father who is worried about his daughter having sex (it's an old joke and we should probably work on an update) and when it happens, he collapses--with relief. "Thank god the worst has happened," he thinks, "now I can get on with my life." Similarly when I hear that people rejected or fought off plans to dam a river and turn the Hetch Hetchy Valley into a reservoir lake in 1903, '06, '09, et al., I'm pretty much just waiting for them to dam the river. If you win the fight for conservation today, very often you're just going to have to fight it out again tomorrow. (Unless you can change enough people's minds or change the situation. Anti-poaching patrols are good; convincing people that ivory isn't cool is better.)
This piece by John Muir was published in book form in 1912, but some part of it was first published in Sierra Club newsletter form between 1906 and '09, and was part of Muir's (temporarily) successful campaign to prevent San Francisco from damming the valley and creating an artificial lake. And it still shows its newsletter roots, I think: along with a Muir-ish description of the valley's beauty, most of this piece is taken up with the argument against drowning the Hetch Hetchy.
Muir's argument for preserving HH Valley leans curiously on one major point: Hetch Hetchy is comparable to Yosemite. I understand part of the logic of that comparison--which he makes several times in this piece: You all know how great Yosemite is, but did you know there's this other great valley? Of course, the downside to this argument seems apparent to me: If we already got us one good valley-and-falls, what do we need another, smaller one? Sure, Muir and his friends don't see that downside--but with a piece like this, you're not trying to convince the conservationists, but the middle-of-the-road people. (Or you shouldn't be; but this narrow appeal might be explained again by this piece's earlier life in a Sierra Club newsletter.)
(Also, Mr. Muir, I'm not sure you're going to convince people to preserve HH by referring to its "airy-fairy beauty.")
But that to the side, Muir's case is wider than just that. Just as he bangs home the point that HH is a mini-Yosemite, he hammers home how "commercial" and limited this project's benefits would be, pushed by "despoiling gain-seekers and mischief-makers of every degree from Satan to Senators... with schemes disguised in smug-smiling philanthropy...". And that's even before he gets around to comparing them to the money-changers outside the Temple who raise up the Almighty Dollar at the expense of God.
Muir even makes the smart move of ending his piece with something of a refutation to frequently-made arguments for damming the HH. So if you read this, you can take it out with you and engage in debate with your pro-dam family, friends, and representatives.
But over all, the argument here is Muir's usual argument for the intangible: people need access to nature--peace, beauty, serenity. Even the urban poor try to keep some nature around them, says Muir, in their little windowsill gardens. And his final paragraph is a final outpouring of anger and love that should really go on t-shirts or bumper stickers:
Dam Hetch Hetchy! As well dam for water-tanks the people's cathedrals and churches, for no holier temple has ever been consecrated by the heart of man.