It might not have seemed like such a bad idea back in 1872. Today, however, things are vastly different. Low-grade ore can't be profitably mined with tunnels. Today's gold mines are strip-mines. The end result of a modern gold mine is a really big pile of cyanide-laced rock and a really big hole in the ground.
Miners reduce entire mountains to huge piles of crushed rock.
Then, they spray cyanide on the piles to leach out tiny amounts of gold. Giant holes and giant piles of poisoned rock are not great for the environment, and they are really hard on our National Forests. In our case, all the gold was on private land next to the National Forest. In sum, the modern application of the 1872 law allows a lot of environmental degradation that its authors couldn't possibly have foreseen. The only permanent solution is to get Congress to bring this law into the modern world.