I know I'm not a 100% selfless altruist. I don't donate all my money to charity and I'm not going to risk going to prison to sabotage a power plant. But that doesn't mean I can't aspire to being more altruistic or want the world to be more utilitarian.
Almost all of EY's posts are about how your gut reaction to things is often wrong, inconsistent, or leads to outcomes you probably don't desire. E.g. Scope Insensitivity (http://lesswrong.com/lw/hw/scope_insensitivity/) where people will pay more money to save 4,500 people out of 11,000, rather than 4,500 out of 250,000.
If someone invites you over for dinner and they have a live calf there, nursing at its mother, and they're intending to slaughter it in front of you, it's not the same (to gut morality) as if they slaughtered it the day before, and really not the same as if they just bought some veal at the supermarket (i.e.: paid someone out of sight to do it).
Likewise; buying something that was produced in a way that involved significant human misery and/or death feels awful to gut morality if the sweatshop, diamond mine, or whatever is next door. On the other side of the world? Eh... well this one is $6 cheaper...
Why should it be so different? Well, gut morality isn't logical, at all. It's worth a bit of effort to do better.
Short of that, it's just a mind puzzle, "how does what I think my beliefs are match up with what I think my beliefs are" or so.