When you have certain groups, in the US for example, preaching that "slavery wasn't SO bad..." maybe an occasional reminder is warranted. I mean, seriously. Have you seen PragerU lately? There's saying the quiet part out loud and then there's cartoon Christopher Columbus outright saying "slavery is better than death."
If you don't like political messages in media, stop consuming media (it's all political in some way these days). If something makes you mad, try stepping back for a bit and work out WHY it makes you mad exactly. And if "slavery is bad" is the problem message for you, maybe you're the problem. Go play a slave training game, or better yet, download HS/HS2 and make your own story. Rub those last 2 brain cells together and pray for a spark of creativity.