You're arguing that the actions of individuals have no impact on the collective actions of humanity, the sum of 8 billion individuals.
Similarly, you probably never had a conversation where someone said "Gee, I'll stop burning fossil fuels now!" But when you use public transportation, or patronize businesses on foot, policy makers are motivated to continue supporting such options. Not for you personally, but for you and others like you.
Maybe it will even happen before California HSR!