Not all of them, especially in recent years. However, those that still fall into that pattern are just as deserving of criticism, and my previous comment applies to them as well. I don't what you were expecting to hear.
Also, Jaxx herself chose to stop serializing the manhwa. That wasn't a decision made by the readers who were criticizing the story from different perspectives. It's not the norm, nor is it fair to use that case to dismiss people who were genuinely uncomfortable and hurt with the premise.

"So people drawn the line at racism but not rape"
Literally any author can talk about these things whenever they want. It's ridiculous to think that you can't talk about real-life issues in fiction.
Just so you know, fiction isn't just made up stuff. It can also be a critique of how reality can change through it, or an analogy of who we are. These topics are sensitive, but they're being talked about in the media because they're part of society. This isn't a "gotcha" moment.
The problem wasn't that Jaxx decided to make a story about slavery, but how she did it. She openly admitted that she hadn't prepared for it, and it looked like it was going to be a total disaster.