How can you assume I've seen it once and am making an assumption? I haven't seen it once. I've seen it time and time again, I just don't have the time to state every example.
The difference is the ability to see a number, and if that number isn't up to their standard. The guy in Fractal literally said 'your DPS numbers aren't good enough for me'. The DRG was clearly a fresh 60 with low level gear. If he wasn't parsing, he wouldn't have known his DPS (or mine) and probably wouldn't have said anything and just got on with the run.
I don't even have to argue against this when the very reason people get banned for using a parser is because they've been reported for harassment. Also, swearing, insulting, and trying to belittle someone is harassment, not a 'disagreement.'