That's not it. It's unlikely that my individual actions are going to destroy the environment, but I don't litter or run the water while brushing my teeth, because it's important that people as a collective not do those things. With politics, I don't vote not because I doubt that collectively we could have an impact, but because I'm quite happy with the trajectory of things as it is.
I should add that your explanation for why you don't vote doesn't seem compatible with your explanation of why you don't litter. Don't you think that if people collectively didn't vote because they are happy with any likely result, those likely results would get pretty bad? Without my addition (regarding the small chance of your vote impacting the election), it seems like you should (according to your reasoning) still do a lot of research to find the better option and then vote for it, even if the difference between options is very small, because if people collectively did no research and didn't vote, the results would presumably be bad.
I negatively affect the environment simply by existing, and routinely do so to increase my comfort level far above what is "necessary" to survive and even far above the average comfort level of humans. I also tend to refrain from littering and water wasting, and I believe that it is important for people to collectively to likewise refrain, but it is irrational to say that the former is a consequence of the latter, since I only have control over my own actions.
