Slaves, accept the authority of your masters with all deference, not only those who are kind and gentle but also those who are harsh. - Peter 2:18
You have to read all the books together from beginning to end. Otherwise you miss the context and overall message.
The Bible is like the movie The Sixth Sense. Once you know what the ending is, all the stuff that comes before it is seen in a completely different way. You are going to look at the exact same words much differently when you go back through the second time, same as you do with the movie.
And that quote you took out of context is not even a bad one. Peter is writing a letter to people, some of whom are in shitty situations out of their immediate control -- slaves, or it is also translated as servants. He is telling them to just bear it with grace because their reward will be in the afterlife.
The parts that actually condone slavery are in the Old Testament. You should at least pick those out. Leviticus explicitly condones slavery in certain conditions, but like I said before, read the Bible all the way to the end and then reread Leviticus to see the same words in a different context.