Someone asked me about this problem recently:
The argument goes like this: If you talk about them, post about them, etc., you're telling their stories for them. Which means you're acting as if you're in a superior position--as if you know more about them than they do.
You could be that way with everyone, which would mean you're arrogant, paternalistic, egotistical, a know-it-all, etc. But they suggest you're that way with Natives in particular because you're a racist.
In short, talking about them = drowning them out = silencing them = disliking them = racism.
I'm not saying this chain of "reasoning" is valid. Far from it. I'm just saying this is the way some people think.
For more on the subject, see Why Write from Indigenous Viewpoint? and Checklist for Friends of Natives.