Let’s say I believe it would be good for my health to go running every day. But I quickly realize that I don’t want to run every day, and that realistically I’ll only run a few times a month. It’s embarrassing to think of myself as being inconsistent, so perhaps I decide that running isn't actually good for my health after all. In short, I come up with new beliefs to suit the action I was already planning to take.
It's obviously silly to come up with new "facts" for the sake of convenience. Is it any better to come up with new moral beliefs for the same reason?
Sometimes I hear people say, "It seems reasonable to believe that people on the other side of the world matter as much as anyone else. But if I believed that, I should be trying a lot harder to help them, and that would require drastic changes to my life. So that's why I don't believe we have the same responsibility to help everyone." This way their actions are consistent with their beliefs—or at least, their beliefs are consistent with their actions.
Let’s take the question, “Is it wrong for me to eat meat?” Upon hearing the question, I immediately translate it as, “Do I want to stop eating meat?” The answer to that is, “No, I want to keep eating it.” So it’s tempting to answer the first question as, “No, animals don’t really suffer, so it’s fine for me to eat meat.” Very tidy.
Inconsistency, in addition to feeling icky, opens you up to criticism. People love to catch vegetarians eating things they’re “not supposed to,” while catching an omnivore eating a turkey sandwich gives no such pleasure. People love to criticize Peter Singer because he wrote an essay saying we should give money to poor people rather than buying new clothes and cars for ourselves, and yet he personally doesn’t wear rags or live in a hovel. (People rarely talk about the fact that he would find it harder to work as a professor and would persuade fewer people if he wore rags.)
And yet people might accomplish more good if they were willing to set high goals and fail sometimes. Give yourself permission to go partway. I’ve often heard people say, “I couldn’t be vegetarian because I’d miss [particular food] too much.” I felt that way about ice cream. So I spent a summer eating vegan - except for ice cream. It was morally inconsistent, and it felt much less morally pure to say, "I'm eating vegan ...um, except for ice cream," but it resulted in me eating far fewer animal products than I usually did.
And maybe if I'm honest about what I believe is right, someone else with more willpower or different life circumstances will be persuaded and go farther than I will. Certainly Peter Singer has persuaded many people that giving money is a good thing to do, even if he hasn't given away every last penny of his own.
In the end, it’s about what your goals are. Is your goal to be able to take pride in how consistent you are? To be irreproachable because your standards for yourself are low enough that you can easily meet them? Or is it more important to be honest about your moral beliefs and actually make some progress toward them, even if you don’t get everything done as well as you would like to?