I mean, it hasn't been for everyone. The reason it is for Wizards is that they have a very conservative fanbase when it comes to the product and thus they try to split the difference by making quiet half-changes that end up pissing everyone off in the end. I mean, I remember reading the critiques of ToA and they are generally speaking pretty simple ones. I could link to a few, but generally speaking they're just asking for depictions of minority cultures not to be an afterthought.
This is a conversation I'm not in the mood for, so I will agree that slavery should be depicted as bad, but ultimately you shouldn't depict it unless you are really ready to deal with it and not just use it as an adventure hook.
Okay, and there are a lot of racist tropes wrapped up in the same sort of image. I'm not sure how I can explain this further.