So, utilitarianism isn't true, it is a matter of taste (preferences, values, etc...)?
Saying utilitarianism isn't true because some people aren't automatically motivated to follow it is like saying that grass isn't green because some people wish it was purple. If you don't want to follow utilitarian ethics that doesn't mean they aren't true. It just means that you're not nearly as good a person as someone who does. If you genuinely want to be a bad person then nothing can change your mind, but most human beings place at least some value on morality.
You're confusing moral truth with motivational internalism. Motivational internalism states that moral knowledge is intrinsically motivating, simply knowing something is good and right motivates a rational entity to do it. That's obviously false.
Its opposite is motivational externalism, which states that we are motivated to act morally by our moral emotions (i. e. sympathy, compassion) and willpower. Motivational externalism seems obviously correct to me. That in turn indicates that people will often act immorally if their willpower, compassion, and other moral emotions are depleted, even if they know intellectually that their behavior is less moral than it could be.
If you have ever purchased a birthday present for, say, your husband instead of feeding the hungry (who would have gotten more utility from those particular resources), then to that extent your values are not utilitarian (as demonstrated by WARP).
There is a vast, vast amount of writing at Less Wrong on the fact that people's behavior and their values often fail to coincide. Have you never read anything on the topic of "akrasia?" Revealed preference is moderately informative in regards to people's values, but it is nowhere near 100% reliable. If someone talks about how utilitarianism is correct, but often fails to act in utilitarian ways, it is highly likely they are suffering from akrasia and lack the willpower to act on their values.
Even if you could measure utility perfectly and perform rock-solid interpersonal utility calculations, I suspect that you would still not weigh your own well-being (nor your husband, friends, etc...) equally with that of random strangers. If I am right about this, then your defence of utilitarianism as your own personal system of value fails on the ground that it is a false claim about a particular person's preferences (namely, you).
You don't seem to understand the difference between categorical and incremental preferences. If juliawise spends 50% of her time doing selfish stuff and 50% of her time doing utilitarian stuff that doesn't mean she has no preference for utilitarianism. That would be like saying that I don't have a preference for pizza because I sometimes eat pizza and sometimes eat tacos.
Furthermore, I expect that if juliawise was given a magic drug that completely removed her akrasia she would behave in a much more utilitarian fashion.
As for the former, I have requested of sophisticated and knowledgeable utilitarians that they tell me what experiences I should anticipate in the world if utilitarianism is true (and that I should not anticipate if other, contradictory, moral theories were true) and, so far, they have been unable to do so.
If utilitarianism was true we could expect to see a correlation between willpower and morally positive behavior. This appears to be true, in fact such behaviors are lumped together into the trait "conscientiousness" because they are correlated.
If utilitarianism was true then deontological rule systems would be vulnerable to dutch-booking, while utilitarianism would not be. This appears to be true.
If utilitarianism was true then it would be unfair to for multiple people to have different utility levels, all else being equal. This is practically tautological.
If utilitarianism was true then goodness would consist primarily of doing things that benefit yourself and others. Again, this is practically tautological.
Now, these pieces of evidence don't necessarily point to utilitarianism, other types of consequentialist theories might also explain them. But they are informative.
As for the latter, according to my revealed preferences, utilitarianism does not describe my preferences at all accurately, so is not much use for determining how to act. Simply, it is not, in fact, my value system.
Again, ethical systems are not intrinsically motivating. If you don't want to follow utilitarianism then that doesn't mean it's not true, it just means that you're a person who sometimes treats other people unfairly and badly. Again, if that doesn't bother you then there are no universally compelling arguments. But if you're a reasonably normal human it might bother you a little and make you want to find a consistent system to guide you in your attempts to behave better. Like utilitarianism.
In March 2009, Tyler Cowen (blog) interviewed Peter Singer about morality, giving, and how we can most improve the world. They are both thinkers I respect a lot, and I was excited to read their debate. Unfortunately the interview was available only as a video. I wanted a transcript, so I made one:
From there I pull back to saying "what does this mean about the problem of world poverty, given that there are, according to Unicef, ten million children dying of avoidable poverty-related causes every year?" We could save some of them, and probably it wouldn't cost us much more than the cost of an expensive pair of shoes if we find an effective aid agency that is doing something to combat the causes of world poverty, or perhaps to combat the deaths of children from simple conditions like diarrhea or measles, conditions that are not that hard to prevent or to cure. We could probably save a life for the cost of a pair of shoes. So why don't we? What's the problem here? Why do we think it's ok to live a comfortable, even luxurious, life while children are dying? In the book I explore various objections to that view, I don't find any of them really convincing. I look at some of the psychological barriers to giving, and I acknowledge that they are problems. And I consider also some of the objections to aid and questions raised by economists as to whether aid really works. In the end I come to a proposal by which I want to change the culture of giving.
The aim of the book in a sense is to get us to internalize the view that not to do anything for those living in poverty, when we are living in luxury and abundance, is ethically wrong, that it's not just not a nice thing to do but that a part of living an ethically decent life is at least to do something significant for the poor. The book ends with a chapter in which I propose a realistic standard, which I think most people in the affluent world could meet without great hardship. It involves giving 1% of your income if you're in the bottom 90% of US taxpayers, scaling up through 5% and 10% and even more as you get into the top 10%, the top 5%, the top 1% of US taxpayers. But at no point is the scale I'm proposing what I believe is an excessively burdensome one. I've set up a website, thelifeyoucansave.com that people can go to in order to publicly pledge that they will meet this scale, because I think if people will do it publicly, that in itself will encourage other people to do it and, hopefully, the idea will spread.
Immigration as an Anti-Poverty Program
I don't think we could have open borders; I don't think we could have unlimited immigration, but we're both sitting here in the United States and it hardly seems to me that we're at the breaking point. Immigrants would benefit much more: their wages would rise by a factor of twenty or more, and there would be perhaps some costs to us, but in a cost-benefit sense it seems far, far more effective than sending them money. Do you agree?
Changing Institutions: Greater Tax Break for True Charity
Millennium Villages Skepticism
Chinese Reforms
Military Intervention
Colonialism
Aid without stable government
Genetically modifying ourselves to be more moral
Problem areas in Utilitarianism
Is Utilitarianism independent?
Peter Singer: Jewish Moralist
What charities does Peter Singer give to?
Zero-Overhead Giving
Moral Intuitions
Improving the world through commerce
What makes Peter Singer happy?
Human and animal pleasures
Pescatarianism
(I also posted this on my blog.)