I can somewhat understand if you've never heard it if you've only been spoon-fed the happy-friendly verses in church sermons. They tend to shy away from the genocide, misogyny, slavery, etc. But you can be sure that they're in there, and they're quite horrendous.
To think that there is only one line in the bible that is horrible and/or outdated is being obtuse. You DO know that there are many MANY problematic verses that just don't work well in todays society, correct?
Here's just one for a sample. If you're hungry for more, I'll gladly teach you:
"You shall acknowledge no God but me. . . . You are destroyed, Israel. . . . The people of Samaria must bear their guilt, because they have rebelled against their God. They will fall by the sword; their little ones will be dashed to the ground, their pregnant women ripped open." (Hosea 13:4, 9, 16)