There are so many forms of slavery that you can't really generalize. Islamic domestic slavery, for instance, was not comparatively bad (although the way you became as slave was most likely pretty horrible). There was no social opprobrium attached to status as a slave, and your social standing usually rose to the level of the household you served in, and very many domestic slaves married into their owner's families. You were subject to your master, but you had rights he had to respect. Janissaries and Mamelukes were slaves, but they also ruled their respective empires. Likewise, the marriage rate for Circassian harem slaves into Pasha rank or higher was an astonishing 60%, to the point that you actually had the bizarre situation that girls would run away from home and sell themselves into slavery (of course this was only open to pretty girls). Slaves had property rights, too, so slaves could own their own slaves, who could own their own slaves.