Dear Dave,
When I was a liberal in the 60's, I was a big supporter
of ZPG. I'm sure they have a website.
CEI and PERC are good libertarian environmental groups.
A quick google search should bring up their URLs.
Any book by Julian Simon would debunk the ZPG line,
for example, _The Ultimate Resource_. Laissez Faire
Books carries most of his works.
Best, Michael