Originally Posted by Baramos
In the original draft script of Batman Begins Goyer kept in the comics version of Ra's/League of Shadows goal of keeping civilization from getting out of hand. It isn't just Gotham being corrupt, it's that Gotham as "the greatest city on the planet" is a symbol of Western capitalism/civilization and therefore needs to be destroyed. It's the same reason they "sacked Rome, loaded plague rats on ships, burnt London to the ground" etc. They equate "modern civilization" (at whatever point in history they're in) with this corruption. It will inevitably corrupt men that live in it so it needs to be destroyed.
We got a little bit of this with Ra's in Begins ("this is not how man was meant to live" talking about balance, etc.) but a lot of the greater eco-terrorist bits of Ra's were cut out of the final shooting script. In any case this is also in TDKR since Talia is obsessed with the free clean energy project that would have solved a lot of the "modern world"'s ills. Of course it was revealed that she wanted to use it as a weapon, but there was still this environmentalist aspect to her character.
This is actually a pretty good explanation. I didn't think of it like that. Now that I think about it, Ras says something about having to address the cities that have reached the pinnacle of their civilisation. Perhaps the LOS believed it needed to be destroyed regardless of whether it is corrupt.