1. I do not think a country's culture can be changed. Name one country that has changed its national character. Americans are still Americans, Brits are still Brits, French are still French, Japs are still Japs. Nazi Germany only changed after the total defeat of WW2. Rwanda only rebuilt itself after genocide destroyed it as a society. The US turned its back on slavery only after civil war. Unfortunately, history shows that a people will not change their character until a deep and profound crisis point is reached.
2. Perhaps nations and cultures are the wrong level of organization to be looking at. If you switch the question to: can you name an individual who changed overnight to avert a crisis? Well, that is quite rare, but now we are talking about the realm of possibility. We can go several levels up from there and talk about dyads and families, and there is still a possibility of change, but it gets more unlikely as you increase group size.
3. The challenge with activist movements is the disillusionment that sets in afterwards. Activists work towards a victory line. But social progress is never about achieving victory. It is an ongoing process. Victory is never fully achieved.
4. If the activist can be disillusioned, then more so with the people whom the activist tries to convert. I am reminded of the scene in Schindler's List, when Schindler manages to convince Amon Goeth that true power is forgiveness. Amon spends a day forgiving people, but then all it takes is one disappointing outcome, and Amon reverts back to shooting people.
5. I am talking about culture, not policy. Policies can be changed overnight. For instance, the détente between the US and China in the 70s is an example of a sudden shift in policy between two of the largest nations in the world. None of what I say argues against the worthiness of, say, trying to campaign for pro-gay legislation, or changing the government's policies towards helping lower-income groups. Policies are more easily changed than culture.
6. We should not try to change society to conform to our ideals. Neither should we conform to society. There must be some middle ground that we can stand on. We should ask each person what they want, and understand them better. Maybe they don't want to be participative. And maybe that's ok. I know that if someone cajoled me into joining some street demonstration, I'd probably be annoyed. Are there other ways we can engage people on an equal footing, and accomodate different styles of being?