WHM not popping Cleric Stance and fast-clutching into Holy with Swiftcast is simply a waste.

You can get what, 8? Seconds where the tank isn't being hit, and shave off 1/3rd of the mobs health. Its a massive help, even vs just three mobs, though its far more worth the MP cost when its a large group.

There is literally zero reason to not do it, there are only pro's and no cons. The mobs are stunned, they die faster, the tank is safe.

People also need to place themselves in the situation, how would you feel about a bard simply auto attacking? Monks who dont move around the mob? WHM who stands there picking nose while a maxed out tank is barely shaving away health.
It is /rude/ to not be putting forth at least a marginal amount of effort if everyone else is.