He also wants to argue with those who say that the good is "limited" or defined, while pleasure is "unlimited" or undefined.
So the good can never be more or less in degree—it always just is the good. Can't get any better or worse and remain what it is. But pleasure isn't like that. It can be more or less and still be pleasure.
Aristotle says that this is not so of the good. Virtues can certainly appear in people to greater or lesser degrees. And while pleasure has degrees, that doesn't mean it isn't defined.
Pleasure-haters would also say that the good is a complete thing (needing nothing else for perfection), but that pleasure is a motion or process.
Aristotle disagrees with this labeling. If pleasure were a motion, then it would be subject to speed (quickness or slowness). One cannot feel a pleasure quickly or slowly, really.
He argues against pleasure being a process of coming-into-being because they don't admit process—the depletion and replenishment of things in the body and mind.
To those who consider that naughty pleasures are the only kind out there, Aristotle thumbs his nose. Those kind of "pleasures," he says, aren't really pleasures at all.
They would only be pleasant to degenerate people. In which case, they'd be painful to decent people. Shameful things can't produce pleasure.
He also raises an analogy used by opponents of pleasure: a true friend vs. flatterer is to the good vs. pleasure.
This means that a true friend's actually the good thing, whereas a flatterer is all about pleasure and nothing else.
And finally, there's the argument that we would aim at many things—including the virtues—even if they didn't give us pleasure.
That pretty much sums up the major arguments against pleasure as a candidate for the good.