This is almost comical, as none of you know Mercy as I do.
Neither does anyone who meets her for the first time.

But seriously, I don't think anyone is doubting whether or not she knows anything, but rather pointing out that in the real world - right or wrong - folks make assumptions about everyone they meet in every situation. You have the choice of wishing that wasn't true, or understanding the dynamic and doing something to overcome it. One approach will help, the other is just "wishing." (Rolling of eyes is somewhere in the middle strategically, but a lot closer to the "wishing" end of the spectrum.)