FFVII: Time Guardian

it's funny that Barret can blow up things and then extract resources, since as leader of Avalanche he should do the opposite...

While it is not mentioned which kind of resource you can extract, I don't think Avalanche was against the fact of using resources for building things. They were against to extraction of Mako Energy, because it was vital to the Planet. We could do a similar analogy about people who are against oil or coal extraction because it pollute too much (including me). However these people are not for the most part primitivists that are against any kind of resource extraction.