Intent vs. Impact is typically the root, at least in my limited experience. Both are equally important and seldom discussed between the offender and the offended. Few people lack the self awareness to perceive how they will be received.
Personal anecdote: I dated an Eritrean-born woman for about 4 months and it was one of the more educational experiences I've had when it comes to examination of my own blind spots. Something as simple and innocuous as complimenting her accent was something I'd not ever given thought to. I'd never considered the impediments her accent had created her, but fortunately, she was very gracious in her explanation. Was she being oversensitive? Perhaps. Was I being ignorant to something that could have been expressed more thoughtfully? Absolutely. I think microaggressions live somewhere in that area between well-intentioned and oblivious, and they are something I dismissed pretty cavalierly prior to that.
Articles like this, however, do very little to actuate any kind of change and seem to exist only to condemn. Understandable frustrations aside, semi-anonymous castigating of white people isn't furthering the conversation.