[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.