Where (literature) would you recommend I start if I wanted to explore the intuition that the practice of philosophy makes/could (if proper) make philosophers better moral agents? Thanks.
There are lots of different answers to this that have been offered:
The idea that someone can be a better moral agent requires first there being a notion of being a better moral agent. Many philosophers have rejected that there is such a thing - that is, that moral behavior is merely a result of cultural or practical norms. "Being morally better" is only a name we put on behavior we happen to like.
Some philosophers seem to claim that philosophy does make one a better moral agent. As Jo Wehler mentioned, Socrates/Plato agree with this: in addition to Symposion, it is also discussed in the Republic. Aristotle spoke in Nicomachean Ethics of the role philosophy plays in becoming more moral (along with habituation to a moral life). Marcus Aurelius in Meditations lists several people who he sees as having improved his moral behavior as a result of the lessons he's learned from them. Augustine also discusses in Confessions the role Cicero's work Hortensius played in his turning away from a sinful way of life. Many in antiquity would agree with the proposition.
There are philosophers in the Christian tradition who point to Paul's letter to the Romans ("I hate what I do") to say either that (a) philosophy does not make you a better moral agent (this was held especially by certain early Christians like Tertulian, but other later, more devotional, works such as that of Louis de Montefort think philosophy merely a distraction), or (b) philosophy can help, but does not lead to perfect happiness (Aquinas is an example of a proponent of this).
In all, it seems the answer to this depends on first answering what qualifies someone as a better moral agent: is it through a life of quiet contemplation (Cicero), obedience to divine law (Tertulian), actions themselves (Aristotle), or merely a convenient name we put to someone acting in a way we like (nominalists)?
You might find this blog post by Eric Schwitzgebel interesting. He conducted a series of empirical studies to try and determine if professional ethicists behaved more morally than others. His conclusion:
Ethicists do not appear to behave better. Never once have we found ethicists as a whole behaving better than our comparison groups of other professors, by any of our main planned measures. But neither, overall, do they seem to behave worse. (There are some mixed results for secondary measures.) For the most part, ethicists behave no differently from professors of any other sort – logicians, chemists, historians, foreign-language instructors.
One of the things that I found most interesting was that the data showed that ethicists "embrace[d] more stringent moral norms on some issues, especially vegetarianism and charitable donation," but didn't actually behave any better with regard to those issues. In other words, ethicists were more likely to believe that eating meat was immoral, but just as likely to eat meat as everyone else.
He doesn't claim that the data explains why this is so, but his personal theory is this:
Genuine philosophical thinking critiques its prior strictures, including even the assumption that we ought to be morally good. It damages almost as often as it aids, is free, wild and unpredictable, always breaks its harness. It will take you somewhere, up, down, sideways – you can’t know in advance. But you are responsible for trying to go in the right direction with it, and also for your failure when you don’t get there.
I tend to agree with William James' take on the subject in The Moral Philosopher and the Moral Life:
The ethical philosopher, therefore, whenever he ventures to say which course of action is the best, is on no essentially different level from the common man. "See, I have set before thee this day life and good, and death and evil; therefore choose life that thou and thy seed may live"--when this challenge comes to us, it is simply our total character and personal genius that are on trial; and if we invoke any so-called philosophy, our choice and use of that also are but revelations of our personal aptitude or incapacity for moral life. From this unsparing practical ordeal no professor's lectures and no array of books can save us. The solving word, for the learned and the unlearned man alike, lies in the last resort in the dumb willingnesses and unwillingnesses of their interior characters, and nowhere else. It is not in heaven, neither is it beyond the sea; but the word is very nigh unto thee, in thy mouth and in thy ear, that thou mayest do it.
You may also be interested in John Dewey who had a theory of the value of ethics and philosophy in education. His book Moral Principles in Education is an important work. This essay on Deweyan Ethics describes some of his thought on the subject as follows:
Because all ethical systems are one, including school and “life,” the “central theme in Dewey’s ethics it is that the application of intelligence to moral problems is itself a moral obligation” (Putnam, 2006, p. 271, emphasis in original). Through the process of intellectual inquiry, individuals can empirically evaluate the given effectiveness of one action over another in terms of the “common good” that each particular action brings about. Individuals have an obligation to put moral ideas “to the test” not by blindly receiving knowledge and accepting it, but rather through examining whether or not certain decisions have definitively positive impacts on the community.
As the essay describes it, Dewey was someone who argued that intellectual inquiry could lead individuals to have a greater impact on the "common good."
It was Socrates - as portrayed by Plato in his work Symposion - who claims that understanding what virtue is makes people virtuous. E.g., see Symposion 212a. But in the same work Alkibiades, who once was a pupil of Socreates, confesses that he himself was not able to act virtuously, despite having been taught by Socrates (216bf.)
Accordingly I recommend Plato's Symposion as an introductory text to the question whether philosophy makes men virtuous.