Hedonism is the proposition that happiness is the only intrinsic good and stress is the only intrinsic bad. Ethical hedonism, the idea that an action is morally good if the actor's objective was to minimize stress and increase happiness, at least in the long run, necessarily follows from ontological hedonism and ethical hedonism can only be justified by ontological hedonism. If others things besides happiness and stress are intrinsically valuable and dis-valuable then how could you rationalize that the decrease of stress and increase of happiness should be the only moral objective? Ethical hedonist egoists believe that an action is ethical if it increases their happiness alone. Hedonism is not a matter of personal preference, it's a logical claim about what actually is valuable or dis-valuable. Someone who accepts hedonism as being logical may, as a matter of personal preference, promote his happiness over the happiness of other people because he only has access to his happiness, but he cannot regard his happiness as being more valuable than the happiness of other people without resorting to non-hedonist reasoning. His happiness may be greater in terms of intensity and duration than someone else's happiness in a specific scenario but, quantity being equal, he cannot argue that his happiness is qualitatively 'more happy' than someone else's. Happiness, not whatever traits or features distinguish any two sentient beings, is the only thing that's valuable. Saying that you should pursue your happiness alone, as an ethical goal, is equivalent to saying that your happiness alone is valuable. Egoists make the same mistake as J. Stuart Mills did with his idea of a 'hierarchy' of pleasures.

As for saying that we value our happiness alone, since we only experience our happiness, I would argue that happiness/stress can not just be considered valuable or dis-valuable to the minds that experience them alone but valuable period, as experiences in the universe, since the minds that experience stress/pleasure are just illusions experienced by billions of separate neurons in the brain. Since the ego is an illusion, there is no central observer who exists who can value his pleasure more than he can value any one else's. Not one of the neurons in my brain, or the atoms that each neuron is made up of, or the sub-atomic particles that each atom is made up of, is 'me'. If I am the sum total of the parts I'm made up of then I am the same as everyone else, I'm just arranged differently. If the happiness 'I' experience is valuable then the happiness experienced by other communities of neurons in other brains is also valuable, I would realize this truth, this fact, if I had access to those feelings. There is no 'me' who values my happiness or dis-values my stress, these states of mind are valuable and dis-valuable period.