Yes, I worry about that too. But I also worry about the opposite: reinforcing the cynical idea that it’s all pointless anyway, so why bother doing anything.
The way I see it, someone who makes the effort to switch to reusable cups is very likely willing to make another effort. They might just need you to point you in the right direction. For example, the issue of why we make so many non-reusable cups in the first place, where they come from, who has the power to stop them but doesn’t, and how they can be held accountable. Just a suggestion of course! :-)
What if it is all pointless and humanity is just f$%ked? That's a very real possibility at this point. The best scientific evidence suggests that we might still have a chance to avoid the worst-of-the-worst of climate change, but changes keep occurring sooner than predicted and that already slim chance is slipping away as we speak.
What is the ethical way to live staring an unavoidable catastrophe in the face? When can we honestly give up?
Personally I think we should never give up. We are not in a video game with a binary outcome - win or lose. There’s a wide spectrum of possible outcomes, and some involve less suffering than other. I think it’s our responsibility to keep going, and push towards less suffering. If only to make the most of the time we have.
The way I see it, someone who makes the effort to switch to reusable cups is very likely willing to make another effort. They might just need you to point you in the right direction. For example, the issue of why we make so many non-reusable cups in the first place, where they come from, who has the power to stop them but doesn’t, and how they can be held accountable. Just a suggestion of course! :-)