Finally, whereas campaigning really does matter in well structured institutions, voting is very strange – the chance that your vote will, in fact, be decisive is almost zero (usually). Suppose it takes you 30 minutes to vote. Even if you earn minimum wage, it would almost certainly be better to work that 30 minutes, and donate the proceeds to Oxfam. All I can say about this is that most people who don’t vote do not, in fact, spend the time they gain from not doing so working for a wage they donate to Oxfam.
I do agree that if you are the sort of person who is persuaded by this argument, you probably should not vote. Ever. It provides such an utterly ridiculous criterion for what would make a vote "matter" that you would think that people who give arguments like this would pause a moment and say, "Well, now that I say it, that doesn't sound quite right." Under what reasonable, rational conception of voting does voting only matter if your vote, in particular, stands a good chance of being decisive? So that's one part of the argument that gets on my nerves.
But the rest gets on my nerves, too; there is, I've found, a whole class of arguments (particularly popular among utilitarians, but not exclusively among them) which might be called "Oxfam alternative arguments", where an activity is compared to donating to Oxfam (or something similar), or working for a period of time and donating to Oxfam, and the comparison is always, of course, unfavorable to the first choice. But this is silly; there is no way to compare the two activities unless we know the field and standard of comparison. Suppose, for instance, that you value participation in the institutions and traditions of your nation. Then it would be utterly silly to say, in light of that value, that it would almost certainly be better to work to donate to Oxfam than to vote. Even if it were still better to work to donate to Oxfam, it would not 'almost certainly' be so; and it could only be so because some greater value took precedence over the value of participation. So such comparisons are meaningless. Which is better, throwing a birthday party for your daughter or giving all the money to Oxfam? Which is better, typing up a post about whether you should vote or spend that time working and donating the money to Oxfam? Which is better, getting eight hours of sleep, or only four while working the other four to donate to Oxfam? There is no meaning to such vague and indefinite comparisons.