Mercedes Lackey is one of the people who pushed this into the hobby, so I don't have much sympathy from her in that respect.
It is obscene that these people aren't even willing to give an old woman who lived through their ever-changing language poisoning the good faith to assume she just misspoke. But then these people were always evil.
Yeah, considering Lackey's role in this, it's hard to feel full throated sympathy.
That being said, your second line bears some thought: 'good faith' in analysis. They naturally jumped to the conclusion, despite Lackey's long history, that she was racist.
I have two takeaways here: one, it's the same as the policy on TBP with 'the onus is on the poster', which means anyone can interpret anything posted to be offensive. And two, it's indicative of the mentality of these twits. Specifically, the addictive nature of social justice outrage. They gotta get their fix, which means flipping out at anyone and everyone.