Yes - it's not surprising to me that few people are willing to consider adopting or living a 'childfree' lifestyle, only that the suggestion that doing so is an extremely effective way to reduce your carbon footprint is received so poorly.

I would suggest that whether an idea is good and whether it is popular are mostly orthogonal, but also that encouraging people who aren't certain they want kids to not do so is, from the perspective of someone concerned about climate change, a good idea.