This implies that all humans are inherently selfish by nature, and that every action of every human has pure self-motivation behind it.
What of action (or inaction) intended to avoid conflict, even when making that sacrifice means that the person is unhappy? Could you argue that it pleased them to avoid confrontation/trouble/pain even though the end result was not what they wanted?
On the same note, I am having a hard time believing that the avoidance of things is pleasure-inducing. Relieving, possibly, but not pleasing. I have a myriad of emotions, and being pleased is not my only positive one.
One more thing, why would people ever be sad if we did everything for pleasure? Wouldn't we just be like, "I could be sad, but instead I will be happy because that will be more pleasurable?"
Humans aren't inherently selfish, but they feel alone. Things feel good or bad to them individually, their neurological systems are theirs alone. Take babies for example. Imagine there was no law punishing my deeds. Taking care of a baby implies a certain amount of work and sacrifice. If taking care of the baby didn't bring me any pleasure, I'd just leave it there. Why would I care? Why would I be obliged to take care of it, if doing so didn't bring me any sort of pleasant emotion? What in me would compel me to act and take care of that baby? We may be able to exert pleasure from helping and pleasing others, but if those things didn't feel good... why would we do them to begin with?
Going to your other point, I believe that things are unpleasant or pleasant. They feel good, or they feel bad. Avoiding pain is an attempt to maximize the pleasure in our lives. Just like everything else.
People don't choose their emotions. Certainly, everyone wants to be happy, but not everyone can create the circumstances that would make them happy. We spend our lives pursuing happiness, but happiness is, by nature, fleeting. We aren't happy because we can't be. It's not a choice.
Anorexia?
They get more pleasure from looking like they're 90 pounds than they get from eating. Certainly better than whatever your 'will to survive' argument says of anorexia.