Unfortunately most conservationists are actually watermelons. The real reason they want to stop development of many areas is to damage the capitalist system.
These people will do anything to prove that capitalism doesn't work. They will damage the economy, cause unemployment, lie about environmental concerns. It's all justified in the end. The more suffering they cause in a capitalist system, the more attractive their communist alternative looks.
Apparently it escapes these people's attention that environmental destruction is much greater in communist countries. Soviet dumping of high-level radio-active waste straight into the oceans, and China's almost total inaction on air pollution, deforestation and erosion apparently go unnoticed in their enthusiasm for criticism of comparatively green capitalist countries. Most self proclaimed conservationists are not actually conservationists at all.
If these people were really concerned with environmental protection they would use the capitalist system to protect the environment. Further they would recognize that a greater population puts more pressure on the natural environment, and they would oppose policies which increase population (such as larger immigration intakes). The fact that they don't, suggests they have a much closer alignment with other groups who do want larger immigration intakes.
See