These statements from your comment and the parent comment to seem to mean essentially the same thing.
> All that can be perceived as racist is not necessarily so
> It's extremely difficult to determine what negative action is motivated by racism and which isn't
The difference is how likely you are to assume possible racism is actual racism. The "glass half full/empty" metaphor expresses that difference quite well.
I addressed this quite clearly:
If you're not generally at risk of experiencing racism (ie. you are of the majority ethnic group), of course it is easy to rule out. It's hardly a glass half empty/half full type of problem.
A glass half empty/half full metaphor implies that the perception is simply down to personal optimism, which as I said, is clearly a gross oversimplification.
Of course someone who is at risk of experiencing racism is more likely to judge an act to be racist, but that doesn't make them right. In fact, they may be more likely to attribute innocent acts to racism, just as someone who rarely experiences racism is likely to make the opposite judgement more often than is justified.
My point is that we are arguing about something that was already expressed by the parent under what I believe to be a more generous interpretation of their use of that metaphor.