In criticizing utilitarianism (or a hedonic calculus) as the primary way of considering life, I have usually focused on the problem of dealing with conflicts between short-term and individual (or small scale) happiness and long-term (or societal) happiness - and also the theoretical and practical difficulties of measuring and summating happiness.
But another problem is that happiness is conceptualized as an outcome - do this and you will become happy - and therefore to aim at happiness seems to require a great deal of precise empirical knowledge of the cause and effect set-up of the world.
In other words, to be maximally happy, you need to know exactly what will make you happy - you need to know the causes that will have the effect of happiness.
So happiness as a goal becomes a kind of 'science' of learning about, and implementing, the causes of happiness. Indeed, 'implementing' is the key word - once the causes of happiness are known, then morality becomes a matter of applying those causes.
If soma makes people happy, then it becomes a moral duty to administer soma to people. The aim of life becomes ensuring that everybody has soma.
For the Christian, the main aim of life is love - love of God and 'neighbour' (ie. other people). Is love an outcome, like happiness? Is love the kind of thing that is a consequence of doing other kinds of thing?
No, love is not that kind of thing. Love is - to a significant extent- a cause; something that affects what we do.
A loving parent is a different kind of cause than a hating parent; a leader who loves his country is a different kind of cause than a leader who despises his country.
Love is both a cause and an effect - Christians are told to add love to the world, and that more love is the hoped for outcome.
To have love as the primary goal in life does not require any empirical knowledge of cause and effect relationships in life; we can love, we can wish to love - to have love as the primary idea we do not need to do research, do not need to make discoveries about how things work.
Love makes sense as the main goal in life; it is something we can understand; it is just very difficult to attain.