Breh, are you SERIOUS? Let's review in more context.
Breh, it may be a "parable" as you say, but look what he's telling them. Look at verse 40, in particular. "You must also be ready because the Son of Man will come at an hour when you do not expect him.”
Even if this is couched within a parable, it's also a WARNING. He is warning his disciples that they need to be on their best behavior at all times because they will never know when he is gonna show up and be able to see what they're doing.
Then the fun part. Jesus goes into a parable about slaves. Read closely. What message is this parable meant to portray? Who is being compared to who? "The master of that servant will come on a day when he does not expect him and at an hour he is not aware of. He will cut him to pieces and assign him a place with the unbelievers."
If you read this entire chapter in context, then you realize that Jesus is comparing himself to a slave master! The message of this chapter is essentially "Don't get out of line because you never know when I'm gonna be watching, just like slaves who try to screw around behind their masters' backs and end up cut to pieces and beaten"
So what if it is a parable? Parables don't refer to "fake" things. He used the example of the slave master because it was so common and easy to understand, that his disciples could easily relate to it. Why not point to something else if you wanted to illustrate a point? The fact that it is a parable SUPPORTS the idea that this was going on; it does NOT refute it. And the fact that Jesus compares HIMSELF to the slave master shows that he himself doesn't even condemn the idea of the master owning and beating slaves, so of course the Bible author certainly doesn't either.
What you got now, Patches O'Houlihan?