Aside from the fact that you're putting words I didn't say into the your "quotes" of things I didn't say into your argument, you're missing the simple fact that no one is saying they expect the people they play with to do 110 % any of them time (outside of progression statics). Most of us would just be happy with someone who didn't leach and pull less dps then I could accomplish with a single macro, 40 ilvls less gear and no thought put into the process at any point. The reason people keep pointing out the sub 500 dps players is because on pretty much every job you can do more than that just by spamming a 100 potency attack every 2.5 seconds while you're auto attacking.
I literally was curious what it would take to get this low, so I macroed my bard, who was equipped in a mix of 170-195 gear, a combined ilvl of 161 with no head or hands equipped. Using only a heavy shot macro with some of the oGCD skills and buffs my bard puts out over 600 dps in that crap gear. No WM, all I had to do to hit 600 was press 1 button twice every GCD. If my gear was up to date this would have been closer to 850-900 range. Why is it wrong for people to ask for at least that level of effort?
As far as your comments about the players situation:
Off Day - Never said I expect rotational perfection, and I don't believe anyone else who has posted on the issue has stated they do either. People can have off days, and if they aren't holding back the group that's more than fine.
Drunk - Flat out not my problem. If I wanted to hang out with drunk people I'd head to the pub.
Sick kid - I get it, I've had emergencies mid-run too. If it's going to be a hindrance to the party I drop, if it's going to be quick I'll excuse myself in chat. If I'm the other person in the group I'll ask if they need a minute. we're not talking about 1-5 minutes of the dungeon to deal with a problem where you dps goes to 0 or virtually nothing, we're talking about the course of a whole 15-30 minute run where someone is consistently underperforming.
Bad day at work...want to mash buttons - See my comments about the macro above.
Literally the only way to hit under 500 dps is to not be doing anything a really good chunk of the time. If you want to participate in group activities, you should be doing your part for the group, even if it's bare minimum. How many people have complained about enrage on Brute Justice this patch? The party dps requirement is only like 4k, which even if the healers aren't dpsing at all, and the tanks are perma tank stance running 500 dps only requires an average of 650 dps form the actual damage dealers. Despite this low requirement parties are still hitting enrage, sometimes even without anyone dying. Those players causing the wipe are basically expecting everyone else to do literally twice the output they do so they can float along in their happy cloud. Parsers would add some accountability to these leaches.