Naïvely, glass is made from sand and copper is mined. And I can already recycle glass from my house, but not copper. So it looks like an environmental win to me. There may be something I'm missing.
- There's a lot of plastic involved, for either medium
- optical stuff is pretty exacting to manufacture. It's easily possible that it's more energy-intensive to refine the materials, make the lasers, draw the fibers and so on than it is to make the copper equivalent
As a sibling comment noted, green energy probably isn't what we would hope it to be.