This is very true for any lifestyle decision that seems to suggest a more productive way of living to someone else. We naturally feel the need to have our lifestyle habits justified as the right choice. Any threat to that, is a threat to our egos.
A better strategy would be to point out the progress (even if false) that someone is making in living a better life (less TV for example). If you can successfully plant that identity seed in their head, they will feel empowered to continue to cut back. The ego is a funny construct.