The chain of reasoning being discussed in this thread allows me to state my issues with the "tetrapharmakon" and "the katastematic-kinetic" distinction with greater clarity.
Once you accept the premise that whatever is not painful is pleasurable (or any of the other ways of phrasing it by the various translators), you have a premise that is as unalterable and important as saying "nothing exists except atoms and void." You take that premise all the way to the end, and you never allow any deviation from its implications. The final result is that you unalterably take the position that if you are alive and experiencing anything, what you are experiencing is pleasure unless you experience it as pain. You can string as many "What about X?" questions as you like for an eternity, and you will never find an example of something that is desirable in itself which does not fall under the umbrella of the term "pleasure." The height of pleasure is then easy to understand as 100% pleasure and 0% pain. This is the approach that we see in Torquatus in On Ends.
Nothing in the letter to Menoeceus contradicts this. Considered in combination with PDO3, which everyone also accepts to be authentic Epicurus, the interpretation asserted by Torquatus is visible in Menoeceus as well. No doubt the same view was stated by Epicurus many times in texts we no longer have, but thanks to Cicero's Torquatus we have the proposition stated clearly in unmistakeable terms. Epicurean ethics makes no sense unless all types of pleasure - mental and physical - are included under the umbrella of pleasure, and no presentation of Epicurean philosophy is complete without emphasizing this point.
One problem with the tetrapharmakon is that "What is good is easy to get" conveys none of this. Even if we take a charitable view that this is a down-the-line conclusion for those who understand the chain of reasoning that gets you there, the layman is simply not going to understand this. The layman is legitimately going to conclude that Epicurus has some weird definition of "the good" that defies the layman's own understanding of what a struggle is generally involved in life. More likely, and worse when combined with "What is terrible is easy to endure" (I am using the Wikipedia versions that the vast majority of the world is seeing), the layman is going to dismiss Epicurus as hopelessly out of touch with reality.
And even if the layman perseveres past the tetrapharmakon and decides to study further, what is he to think when he is confronted with the endless debating over the "katastematic-kinetic" distinction? What is he to understand from the refusal to translate these terms into the understandable language he speaks today? The whole key to understanding involves explaining that the normal state of life without pain should justly be considered pleasurable. Fixation on untranslated Greek words like "katastematic" or "ataraxia" are treated so mysteriously that the reasonable layman is going to be bewildered. Most of them are going to carry forward their preexisting understanding of the word "pleasure" as limited to "stimulation of the senses," and they are going to conclude that Epicurus has put his finger on some kind of esoteric stimulation of the senses that is so otherworldy that only an ancient Greek can understand it accurately. Yes, some people (primarily academics), find the contemplation of this mystery to be entertaining, but the reasonable layman is not going to think so, and he is going to fully discard Epicurus at that point.
In contrast I would say that Cicero and Cassius Longinus were both correct: Epicurean philosophy in its broad outline is easy to understand. No, there are no supernatural gods telling us what to do. No, there are no ideal forms or essences that tell us what to do. Instead, Nature shows us through the feelings of pleasure and pain what is desirable and what is not. Nature does not give us a fully formed mind, however, and it is up to us to learn to understand that life itself in all its non-painful experiences is pleasurable, and that unless we are suffering some specific pain then we are experiencing pleasure. The wise man will then understand that he has access to all sorts of pleasures, some mental and some physical, that are attainable in all but the most extreme situations of life. While all of these pleasures feel good, the wise man will decide which pleasures to pursue and which to avoid by evaluating the full result of his actions. When all non-painful experiences are placed in the balance of life against the painful experiences, the wise man will see that pleasures can readily be made to predominate over pain, and thus a life of continuous pleasure is possible. Pleasure is not limited only to the rich or fortunate whose circumstances allow them access to luxury and thrills most of their lives, but it remains a valid framework by which even the poor and less fortunate can organize their lives.
The observation that the highest pleasure is experienced when all pain is gone is simply an obvious result of the first premise that the sum total of pleasure is measurable by the absence of pain. If you identify the goal of your life as "Pleasure," and you understand that everything that is not painful is pleasurable, you can never heighten the experience of pleasure no matter how many extra years you might live. Time is always desirable, but the extra pleasure obtained through extra time is just a variation of the pleasures already experienced, and the extra time does not improve the perspective that pleasure cannot be improved once all pain is gone. This also is not to say that you should limit yourself to simple pleasures or pleasures of the mind, but only that when you are evaluating a goal for your life, it is conceptually and understandably valid for everyone to see that in the broadest terms, a life from which all pain is eliminated as a way of measuring the ultimate goal, whether you are an oyster or a cow or a sailor or a general or a philosopher.
None of this is conveyed to laymen by repeating "what's good is easy to get" or stating something like "Epicurus held katastematic / restful / stable / abiding pleasure to be the authentic type of pleasure which is the true goal of life." When academics focus on stating those propositions over, the result may be an increase of their reputation among their academic peers, but they not only fail to bring healing but in fact drive away the legions of ordinary people who would otherwise benefit from Epicurean philosophy.