Why are environmentalists like a watermelon?

Professor Stephen Bainbridge blogged The National Park Service plans to reduce the size of a cell phone tower near Old Faithful, as well as camoflauging it. But that hasn't stopped the whining from the institutionalized environemtal left:

... an activist group, Public Employees for Environmental Responsibility, based in Washington, D.C., wants the Old Faithful tower removed.
"The towers are being put up for commercial reasons, not for public safety," said Jeff Ruch, the group's executive director. (Link)

Does that give you a hint as to the answer to my titular question?

No? It's because they're green on the outside but red on the inside.

Nothing could better illustrate the fundamentally anti-growth, anti-capitalist mind-set of the environmental left than that rather blunt quote from Mr. Ruch.

I agree completely. The environment is important, but so is growth and capitalism, and there needs to be a balance.