Littering makes a difference. It's nearly impossible for one person to notice the effect of one person littering, but it makes a difference to a large number of people.
Voting has a tiny chance of making a huge difference. The probability of the election hinging on one vote is minuscule, but if it happens, you change the president for four years, and make a significant mark on the country. This is orders of magnitude more than the difference you make normally.
Note that that isn't necessarily worth it. I don't know if it is.
In my post I suggested there are two separate motivations for voting:
1) Picking the winner. Essentially no one does this in big elections, but yes there is that tiny chance. I didn't go into this motivation. Thinking about it now I suspect using a lottery-like mentality a lot of people do vote for this reason: they just might be the one.
2) Adding to voter turnout, thus making the election legitimate. Everyone who votes does this, but it's only by a tiny amount. This I would equate to "not littering" in that you are unambiguously helping but o...
For many years I've been interested in the "paradox" that your vote tends to never alter the outcome of an election, yet the outcome is in fact determined by the votes. I wrote a blog post about this and tried to explain it in terms of emergence, we as voters are just feeling what it's like to be just a tiny part of a much bigger system.
Then I tried to explain that "voter turnout" is in fact one of the most important metrics for an election, it determines the legitimacy and stability of the process. So therefore even though your vote won't determine the winner, it will contribute to voter turnout and thus is productive and useful.
http://www.kmeme.com/2010/10/why-you-should-vote.html
However I don't find my argument all that compelling, because even voter turnout is going to be approximately the same whether you vote or not.
In the post I bring up littering as something else where your tiny contribution adds up to be bigger result. I personally would never litter on purpose, yet I often skip voting because it seems like it doesn't make a difference. Is voting rational? How do you justify voting or not voting? My post was non-partisan so I'm soliciting non-partisan comments, trying to focus on the theory behind voting in general.