Healers that don't want to DPS are like DPSes who refuse to move out of AoEs.

[Atos]

If you're not chain healing a massive pull, you have time to DPS. It's not a strawman. You can also stop DPS'ing if you're about to put yourself in a critical MP state (It's a strawman to assume anybody is arguing OOMing yourself with DPS).

The 20/80 is based off a wonderful video that was created by someone in the healer forums and then analyzed and broken down. What it depicted was less than 20% of the time there was Healing casted during pulls, and 80% of the time was doing the Manderville Dance (/mdance).
It wasn't a random percentage pulled out of my ass . But that would have been based off your own assumption, wouldn't it?

It's a strawman because I didn't say anything about chain-healing and you portray it as the only factor, which is not the only relevant consideration.

Though 20/80 is not what I usually do/see during dungeon runs. And there's a method that people use to approve what healer does dps-wise? I'd love to see it. Because it seems to me that it's just "dps or gtfo". Also you seem to be talking about dungeons, whereas what I see is the attitude that healers have to always dps whenever they're not healing, raids included. I see a lot of awfully un-specific blanket statements that people use to justify something they made-up themselves.

Edit:

Ok, looked at the video. Unless there are more that's a pretty small sample size. I admit that it happens, though my experience is generally not quite as smooth. And again, dungeon. Not Alex savage, not Zurvan ex, a dungeon.