You don't understand that (Should) and (Has) to dps are two different things. Nobody is arguing wether a healer should dps or not. This long year issue is whether the healer Has to or not.

Dps has to do damage
Tank has to keep agroo
Healer has to keep the team alive.

A healer should dps yes but he's not forced or obligated to because (Should) and (has) are two different things. Most healers understand this and only dps when they want to and not because people think they (should)