I understand your feeling regarding our small action being useless, I feel the same.
What I try to tell myself to keep doing it is: If most of everyone would do it, that fart in the wind would be loud enough to make politician realise they have to take it into account and pass legislation aligned with that.
Deep down though, I know we'll never be enough to do it for it to have an impact
My employer, employing 90 people, a lot of which are in their 20s and 30s, has decided to organise the yearly seminar event in a place where most of the company needs to board a plane to go. I immediately said I wouldn't go if I needed to take a plane, I was not the only one to say it. The company offered to reimburse any alternative journey (train+boat) which is a bit more expensive, but way way longer (14h transport vs 3h on plane, not taking into account the time in between train and ferry: I'll be traveling for more than 24h in total between start and end, and same for the return journey). I said I'd do it, the others that spoke out: not so much, they are either not coming or taking the plane... In the end I think I will be the only one, we'll see.