The word "passing" seems to be emotionally charged for a lot of people. Personally, I prefer to think of it as blending in. 100% stealth is likely not an option for me, but neither do I want to be visibly or identifiably trans. And from a professional standpoint, I had better be able to blend in if I plan to be continue be able to work with a wide variety of people (I work as a financial consultant). As several people have mentioned, there's a difference between people being supportive of your decision to transition and actually being fully comfortable around you.
I agree with Evelyn. It's ironic that a girl who passes is criticizing those of us who want to.
I think there's a happy medium between this line of thinking that says passing doesn't matter, and the passing is EVERYTHING that the "author" of "so you want to be a t-girl" espouses.