That's not the issue at hand, though. No one is arguing that you must DPS all the time, and it's completely normal if you're conservative with your MP management for the first pull of a dungeon just so you can gauge your group, see if the tank uses cooldowns correctly, see if DPS dodge AoE's. Even if you're DPSing a lot, and you feel like you're going to run out of MP, like you've stated, it's the smart move to stop DPSing because MP management is your job. A lot of people, however, pop Shroud way too late, and Assize does instantly restore a portion of your MP, so WHM does not play like it did in ARR. Pop a Divine Seal, Asylum, and Regen, and the passive healing that your tank will be getting will be really nice, freeing you up to do other things. It's also a lot easier as a WHM now to throw out an "oh shit!" heal coming right out of Cleric Stance with the inclusion of Tetragrammaton into their toolkit, which is an OtGCd heal.We're mainly talking about healers who avoid DPSing like it's the plague, to the point where they throw a heal every 10 seconds or heal bomb you every time you fall below 95% HP, and both are extremely lazy and no one should be encouraging that playstyle.
Tough love is sometimes needed. It is not a healer's responsibility to babysit a DPS who doesn't dodge, just like it's not that DPS's right to hold their healer hostage. Some lessons are learned the hard way.