Earlier quoted context omitted.
Your actions do not, indeed, matter. Neither does your vote, or your boycotting of $global_evil_corp, precisely because there's millions or billions of people involved. (To be pedantic: while not literally zero, your actions matter several order of magnitude less than would be necessary to be able to perceive their effects.) But that's a really hard pill to swallow. Your post is a beautiful example of that difficulty…
So you're saying my neighbors and I should feel fine throwing old car batteries in the lake and switching back to leaded gas?
If leaded gas was still being legally sold alongside unleaded one, people like you would be passionately arguing for decades about why it's everyone's moral duty to pay extra for unleaded gas, and you would feel so proud every time you stopped at the green pump instead of the black one.
And meanwhile we would all be breathing lead.