So if killing people is pleasurable to a serial killer then his well-being is increased by killing people, and, therefore, his killing people is morally good? — WISDOMfromPO-MO

No, at least not necessarily. There's a difference between saying taking pleasure in killing people is good for the person doing the killing, to saying the fact that the person kills people and takes pleasure in it is morally good.

What is good for someone may not always be what is morally good.

If one's well-being is determined by his/her pleasures, and if killing people gives one pleasure, then doesn't reason dictate that his/her well-being is partially determined by killing people?

If well-being and morally good are not connected, how can hedonism be a moral theory?

If well-being and morally good are not connected, how can hedonism be a moral theory? — WISDOMfromPO-MO

It can be the axiological foundation of a consequentialist theory that would take the value of a population as more important than the value of an individual's experiences, as a population is merely a conglomeration of individual experiences, with all individuals being equal to each other.

Or you can focus more on negative experiences, and say that the pleasure that comes from killing people cannot be morally good because it causes negative feelings in others.

Like I said, rational self-interested hedonism =/= morality.

this article — WISDOMfromPO-MO

What sounds best ... "utilitarian hedonism" or "hedonistic utilitarianism"? Whichever, I am its ist.

From later in that article:

Hedonism, as I’ve said, is just a theory of well-being. By itself, then, it has nothing to say about how we should live. Importantly, it does not say we should live so as to maximise our own self-interest – that (false) theory is called egoism.

The IEP article on hedonism draws a distinction between value and prudential hedonism, which seems to be the type talked about in your article, and hedonistic egoism, which seems to be the type you're considering.

By making pleasure an end in itself, hedonism was sure to have its ethical opponents.

I don't think that pleasure can be an end in itself. We always take pleasure in something, it is not experienced except in relationship to something else,

In this article it is stated that, “Simply put, hedonism says that your well-being is fully determined by your pleasures and pains..."

So if killing people is pleasurable to a serial killer then his well-being is increased by killing people, and, therefore, his killing people is morally good? — WISDOMfromPO-MO

One argument for rejecting hedonism.