Grassroots movements and citizen created advocacy orgs (non-profits, etc) can be a big part of what often causes government to make policy changes.
But you are right that the primary focus should be on facilitating effective policy change for such issues.
I do think there is some value in individual change as an agent of broader cultural change, but this is much harder to assess. Part of my reasoning is that policy change will likely fail without some corresponding cultural change as well. I'd like to learn more about this complex dynamic though...
In the end, policy change is definitely necessary to successfully defense against large, negative externalities.