Hunter may not be that good, except as one mentioned easy to use.

Rogue\Druid will be useful for some instance run to farm nice loot, due to their ability to ninja all the way to the boss\chest. Certain mobs do detect stealth easily, so not every instance.

Mage will be better to farm in general setup. AOE, you kill lots faster, loot faster, drink water, mana up, rinse again. Usually this is for farming norm stuffs (in quantity)

Farming gold is just one of the activity expected in the game.

The bad is ppl selling gold.
But then, if there's demand, there are always supply. Practically speaking, unless Blizzard can come up any solid to prohibit this, no point argue it over.

Ppl dont give a damn about moral.