Cutting down trees is not bad in itself. As long as you don’t cut too many trees in one place and don’t replant trees, it’s fine. It’s only when you do massive, destructive clear-cut deforestation (like in the Amazon) that there’s a real impact.
Without materials to build things, the only thing for us to do is hunt and gather, and that’s just not going to work.
It’s necessary for modern society and it won’t stop, but it’s the least of our worries. It’s totally possible to be eco-friendly.