Now that the common claims of the Wise are on the table, we can begin the analysis.
These are pretty much the things that are said. That it does not follow from these grounds that pleasure is not a good, or even the chief good, is plain from the following considerations. (A) (a) First, since that which is good may be so in either of two senses (one thing good simply and another good for a particular person), natural constitutions and states of being, and therefore also the corresponding movements and processes, will be correspondingly divisible. Of those which are thought to be bad some will be bad if taken without qualification but not bad for a particular person, but worthy of his choice, and some will not be worthy of choice even for a particular person, but only at a particular time and for a short period, though not without qualification; while others are not even pleasures, but seem to be so, viz. all those which involve pain and whose end is curative, e.g. the processes that go on in sick persons.
Those processes have changed, but you can still see the point. Generally being cut open with a knife is neither pleasant nor good for you, nor is it good to have a part of yourself cut out; but if you are sick and need surgery to remove a diseased part of yourself, it can be good for you to be cut open with a knife even if it isn't good for everyone. Since it enables a return to health and therefore pleasure, it can even be an activity that is ordered towards pleasure in a way -- though it is unlikely to be pleasant in itself.
(b) Further, one kind of good being activity and another being state, the processes that restore us to our natural state are only incidentally pleasant; for that matter the activity at work in the appetites for them is the activity of so much of our state and nature as has remained unimpaired; for there are actually pleasures that involve no pain or appetite (e.g. those of contemplation), the nature in such a case not being defective at all. That the others are incidental is indicated by the fact that men do not enjoy the same pleasant objects when their nature is in its settled state as they do when it is being replenished, but in the former case they enjoy the things that are pleasant without qualification, in the latter the contraries of these as well; for then they enjoy even sharp and bitter things, none of which is pleasant either by nature or without qualification. The states they produce, therefore, are not pleasures naturally or without qualification; for as pleasant things differ, so do the pleasures arising from them.
Here we can see what Aristotle would make of our affection for hot sauces made out of chilies engineered by American scientists to be much hotter than anything in nature. Just as he says, when you're hungry and are restoring yourself by engaging in appetitive processes, some of the "sharp and bitter" things you might enjoy aren't necessarily pure pleasures in themselves, yet in the moment they can be quite enjoyable.
(c) Again, it is not necessary that there should be something else better than pleasure, as some say the end is better than the process; for pleasures are not processes nor do they all involve process-they are activities and ends; nor do they arise when we are becoming something, but when we are exercising some faculty; and not all pleasures have an end different from themselves, but only the pleasures of persons who are being led to the perfecting of their nature. This is why it is not right to say that pleasure is perceptible process, but it should rather be called activity of the natural state, and instead of 'perceptible' 'unimpeded'. It is thought by some people to be process just because they think it is in the strict sense good; for they think that activity is process, which it is not.
That may be a little opaque because it turns on a logical distinction that isn't obvious if you haven't read more of Aristotle than just this. The difference between an activity and a process here is that a process is a set of things one does in order to obtain something else, whereas an activity is a thing done for itself. Happiness is an activity, i.e., the very eudaimonia we've been seeking in the ethics is something that you do in order to do it. It is, as it were, its own end: we aren't seeking something else by flourishing and being happy, but rather, we are flourishing and being happy just because we want to flourish and be happy.
A process aims at something, and because it does so that something is more important than the process itself. It's worth going through the process, in other words, in order to obtain the end that the process seeks. You might do the work of building a garden in order to do the work of growing tomatoes and peppers in order to do the work of harvesting them in order to do the work of cooking with them in order to do the work of canning the results in order to obtain delicious food that will last through the winter. That's a process with a product. The product is obviously superior to the process because you are willing to go through all the laborious steps in order to obtain it.
(B) The view that pleasures are bad because some pleasant things are unhealthy is like saying that healthy things are bad because some healthy things are bad for money-making; both are bad in the respect mentioned, but they are not bad for that reason-indeed, thinking itself is sometimes injurious to health.
Indeed it is. Havamal 54-6.