You're right, system change is absolutely fundamental for success on the scale needed, but individual choice also needed, and your title is completely misleading ... 'degrowth' is essential, but through systems and values change, not, as you rightfully point out, by just berating individuals.

The same confusion is stated in no less than last weeks Nature editorial, https://www.nature.com/articles/d41586-022-00723-1 where a false choice is presented between degrowth and green growth...we need them both, in different mixes in different places.

If you're interested please see my take, which explains more fundamentally why damaging affluence/consumption must systemically be reduced, whatever label one wishes to use https://www.preprints.org/manuscript/201812.0176/v1