PD3 doesn't say The limit of "tranquility" is the removal of all pains. It says the limit of pleasure is the removal all pain. I won't belabor this, but if there are only two feelings - pleasure and pain - if all of one is removed, you're left with the other.
This is a key observation and very well stated.
Of course, the advocates of "tranquility/ataraxia" as the ultimate goal, rather than happiness based on pleasure as Diogenes of Oinoanda shouted about and Torquatus explains at length, have plenty of arguments up their sleeves. One of the arguments to watch out for amounts to: "It doesn't matter that PD3 refers to the limit of quantity of pleasure. Tranquility/ataraxia is not pleasure at all - it's higher than and better than pleasure, and that's why it is the true goal of Epicurean philosophy. After all, Epicurus says when all pain is gone we have no need of pleasure -- so what else could he mean other than that tranquility / ataraxia is not a pleasure at all?"
The key answer to that is to point out how the tranquility argument begins to expose itself as a death cult argument. PD2 and Epicurus's foundational statements on death say that "Death is nothing to us, for that which is dissolved is without sensation; and that which lacks sensation is nothing to us."
Now you can quibble as well (certain people have no problem quibbling til the cows come home) and say - well "pleasure" is not a "sensation" so that view doesn't count. Ataraxia / Tranquility is not a sensation, but you can experience it while you are alive, and Epicurus is really just channeling the Buddhists and Stoics and assorted ascetics by saying what a wonderful thing it is to be numb.
That argument is nonsense, but if you're the type who reads the sweep of Epicurean texts talking about pleasure, pleasure, pleasure, and there are only two feelings, but you can still come back and say "Epicurus said the goal is ataraxia / tranquility" then your'e the type that just likes to argue and not worry about reaching any productive conclusions. For some people, the argument IS the goal. They could care less that there is absolutely no evidence of ancient Epicureans living the kind of hermitic ascetic lifestyle that they are advocating.
"But Epicurus said all he needed was bread and water and a pot of cheese!" That's a nonsense argument, and Don too has pointed out. It would be more persuasive to argue that Epicurus needed that bread and water to feed his slaves and the accountants he would have needed to manage his properties and handle the schools income and support of others.
The Tranquility/Ataraxia/Ascetic construction of Epicurus is not credible, and no one in the ancient world believed it or argued it. The ancient world understood him to be advocating pleasure, in all its forms, and the best evidence is how the Epicureans lived their own lives. There's not a documentable case anywhere of a single Epicurean setting out with a goal of living as a celibate or in sackcloth and ashes or a hovel or a cave or in isolation or on bread and water.
That entire approach is nonsense, even if it is the consensus of Academia.
