Infants and animals were examples used in ancient Greece to make an argument for pleasure, both "do" and "ought." Today we have neuroscientific research, such as Barrett, Lembke and others, to provide the "do." (I don't have more specifics at hand; just seeing if this will advance the discussion.) Then the task becomes getting to "ought." I've personally never found formal logic at all convincing. I tend toward more practical means, such as "if we understand that pleasure and pain are guides to our behavior, doesn't it make good sense to understand how best to work with them? Why not try it out for a while and evaluate your results?"
But I'm uncertain as to the posts between Todd and Joshua and where they're going....