I'm reading a book by F.W. Bussell called Marcus Aurelius and the Later Stoics which I am inclined to describe as rather angry. The author seems irritated by the fact that Epictetus and Marcus Aurelius in particular are admired by many. He thinks them inconsistent, melancholy, selfish and, perhaps worst of all, "Buddhist" and strives to tell us why. He accuses them of quietism.
As I've noted before, I'm impatient with those who criticize the Emperor as a philosopher on the basis of the Meditations because, as should be apparent to even the meanest intelligence, it is clearly not and was not intended to be a polished work of philosophy propounding a particular position (alliteration brings me joy now and then). The same may be said of the works of Epictetus as we know them, which consist of the notes of his student Arrian. Macus wrote to himself as a kind of spiritual or mental exercise; Epictetus was rendering counsel on a variety of issues having to do with how to live. It seems merely foolish to expect the exposition of a consistent, formal system of philosophy from these works.
The comparison of Stoicism with Buddhism is made fairly often, and makes a certain facile sense. As they were developing at more or less the same time, mutual influence is quite possible. If one considers the fact the Stoicism is intended to be a means to personal tranquility, I suppose it may be described as "selfish" in a broad sense.
This would be to ignore the emphasis of the Stoics on the brotherhood of man, though, and the fact that Stoicism recognizes us to be social beings with obligations to one another. As far as melancholy is concerned, it is also to ignore the fact that Epictetus in particular seems at times to be joyous, calling on us to thank God for our lives and abilities. Bussell acknowledges all this, as he acknowledges that Marcus was a most dutiful and earnest Emperor, but this represents what he believes is the "inconsistency" in their views. They are really, or predominantely, selfish and melancholy, no matter what they profess to the contrary, according to Bussell. It seems he feels that in order to be admirable, the Stoics must be more cheerful, optimistic, but it is unclear how he thinks this is to be achieved.
I think it's fair to say there is a tension in Stoicism as there may be in other systems, as to goals. Tranquility demands an acceptance of things beyond our control and an appreciation of the fact that we must be indifferent to them, and sometimes it seems in the case of Marcus that it may also demand a disdain for our humanity to the extent it consists of the body and our interaction with others (Bussell also sees a connection between Stoicism and ascetic Christianity). It may be that taking a cosmic view of our place in the universe, recognizing the vastness of the things beyond our control, is conducive to a kind of selfishess and quietism.
But I don't think it necessarily does so. One need merely be intelligently realistic. The fact we hold a very small space in the universe, the fact we are human, should be self-evident; nevertheless, it is clear we are human and it is in our nature to have human concerns, desires, needs, experiences. Living in accordance with nature should not mean that we must deny our natures. We are what we are; we are where we are. The issue is how should we live, in the circumstances in which we live. Pretending we are more important (usually far more important) than we are in the universe is not intelligent. Neither is it intelligent to disregard our needs or the needs of others.
Recognizing this is I believe a part of our use of our Reason, which is one of the things in our control. It may be the first step in the use of our Reason.