[bzbarsky]

Why would literate slaves pose a risk to stability, necessarily?

Keep in mind that slavery for these people was nothing like the chattel slavery of the US south. Being an educated slave did mean that you had some restrictions on what you could do; it also freed you from having to worry about food and shelter, say. Similar tradeoffs have been made by salaried workers in Japan in the 70s and throughout the Western world during the industrial revolution

And even the restrictions part was ... varied. If you're a slave and your owner lives in Athens while you live in a Greek city on the Bosporus and supervise your owners business interests in the Black Sea (an actual example I recall from some of the primary sources from my Greek history classes in college), you really don't have much in the way of restrictions on you. Yes, legally you're a slave. So what? It has very little impact on your day-to-day life, at least as long as business is good.

[smhinsey]

I don't think that it's a necessity, but we're talking about the Romans, who are pretty notoriously paranoid about security issues since Rome was sacked by the Gauls. This concern seems in line with what I know of the general attitude of the average Roman citizen, especially if you're talking about slaves that came from the outer provinces, as most did in later years.

I just don't think you can ever be totally secure psychologically while you own slaves, but as I said elsewhere in this thread, there are a lot of things about the Roman mindset that are very difficult for the modern mind to identify with, so at best, this is marginally informed speculation on my part.