I am main WHM for more than a year and half, also I'm a decent WAR.

As a Healer & a Tank, I am in favour and encourage Healers to DPS. I call it an Active Healer Mode, even with heavy healing a Healer can cast the least Aero or Virus, thus helping.

But I encountered Terrible & horrible healers:

1. Only Healing Type:

Me as Tank, I run Deepcroft (normal), Whitemage only casted protect on me & ownself (DPS were watching CS). Her character was always on standing idle pose (hands behind head). Only healed when my HP was lower than 25%, I am a main Healer, so when I tank I avoid/reduce as much damage as possible to ease my healers; yet this Whitemage was a jerk. When I asked for proper healing and to be at least active I got the famous "Do you see yourself dying?" sentence.

2. I'm DPSing Type:

Me as a Lancer in Halatali (normal). Scholar was on Cleric all the time. Tank was GLD (with main whm/sch Lv.50). Tank's HP was draining like crazy, and for a reason Eos's heals weren't enough. The BLM started to heal the tank while the SCH was DPSing (on cleric). This time the BLM asked the SCH to heal and she replied with the famous "Do you see him dying?" sentence. Mind that the Tank died due lack of heals 4 times before reaching the 2nd boss & rage quit.

Note: I respect healers who are over healing more than the waiting with /idle pose. I also respect the active healers who want to help DPS, but not to the extent that they forget to heal (especially scholars.. if you want to DPS que as a SMN not SCH).