Say someone else wants you to switch to wind power. Your electric bill will go up by 60%, but you won't be contributing to climate change with your home electric use. An additional 5 cents per kWh isn't so much, so you decide to do this too.

Another tells you that most chocolate is produced by slaves, and so you should switch to slave-free chocolate, which means organic or fair-trade. It costs three times more, but chocolate isn't a large part of your budget and you can spare the money.

You're now spending some money on virtuous eggs, other money on virtuous electricity, and a bit more money on virtuous chocolate. Each of these is good, but could you do better? Your consumption choices motivated by a desire to improve the world should compete with charities for the place of 'most effective', and whichever wins should get your money. When someone suggests you spend money on a more virtuous version of something, ask whether it is the most good you can do for your dollar.