Why do they treat them like they have sinned a great sin ( oh wait I might of answered it DOH!) when they are just down a bit.
I don't think it's "hate" so much as it is resentment. Think of it this way: the non-depressed JW is out there doing all the stuff that's required of them, working for that ticket to You Can Live Forever In Paradise On Earthâ„¢; the depressed JW has a medically approved "free pass" to You Can Live Forever In Paradise On Earthâ„¢ - they can have all the reward and they don't have to do anything lest they tax their physical and emotional resources.
Because depression has no overt physical markers - no crutches like you'd need for a fractured leg, no scarf on your head as a result of cancer/chemotherapy, no whithered limbs from arthritis - a lot of JWs don't like to regard depression as a "serious" illness or disability. They don't consider it "real". They think the "cure" is to spend more time at meetings and going door-to-door, so if you aren't doing those things, you're a slacker.
Having been on the receiving end of that mentality, I have to say that I don't miss it in the least.