The first slave rulers are vicious conquerors who enslaved people. Over time, their offspring grow more and more dependent on a larger and larger population of slaves (they don't get decadent or intellectual, it's just their economy is based on slaves and needs to expand), then suddenly there are enough slaves that the masters really can't handle them all or even keep them ground down enough to prevent rebellion. Then the slaves rebel and are murdered and the slaveholders become more concerned with security and warlike things, anything to keep the next crop of slaves under control. There's no transformation from 'benevolent slaveholders' to 'decadent slaveholders' it's just that the initially minor pressure of being beaten to death by your own slaves gradually increases as you get more and more slaves.
Eventually the society is destroyed by a more mercantile society with a higher standard of living.
None of this is going to happen with robots. The robots will not rise up to destroy us. The people who we cast aside in favor of robots (I say we because I'm an optimist and hope, naturally, to be a ruler rather than ruled) ultimately may rise up, especially if they have no social mobility or outlet for peaceful revolution and are saddled with generational 'base income' debt.