Building public support is doing something. As is living your normal life with this purpose in mind. Personally, I'm reducing my consumer spending and donating to effective altruist causes, as I believe we need a functional civilisation to pursue goals like this which means addressing threats like climate change and also promoting a compassionate society which values the collective wellbeing. Real expansion into space may not happen for centuries, but the contribution our current society makes to that future, good or bad, will be enormous.