What group or entity is responsible for the ugly depiction of witches? ?

Two Socks - It began in Europe with the culture of the "trained" doctors (who yes were men). They were in competition with the midwives and healers who had great success. http://womenshistory.about.com/od/witches/Witches_and_Witchcraft.htm

It's largely thanks to the Catholic Church. People were holding on to their pagan beliefs and practices, so they demonized them: witches (who were just practitioners of folk medicine and herbalism) became evil hags, and the male pagan deity (the horned god) became the devil. They then adapted festivals and holidays to suit their agenda, making it less embarrassing when the populace could not be stopped from celebrating Ostara, Beltane and Yule. (Easter, May Day, and Christmas)

The first answer is correct. Christians against Pagans. The motivation was to both denegrate the Pagan faith and to demonize female holistic healers. At that point in history any outspoken/powerful women were demonized.

Christianity against Pagans.

It was the catholic church replacing the old religion with their own corrupt systems. You have got the folklore, fairy tale and Disney archetypes too.

You're all wrong. It was the early MRA organizations that demonized the healers and herbalists to discount women that held esteem in the community. They feared that if these women became too powerful, they would start asking for equal rights and control over their bodies and educations.

If you're trying to talk about how evil witches are, it only makes sense to paint them in a way that is undesireable.

Christians

Yes, witches are always viewed as 'ugly old hags' but they came from all ages, class and backgrounds. Young women were often accused of being a witch just because their babies died in childbirth. Birthmarks or any abnormality in appearance, even a simple mole, were deemed as the mark of Satan. Motivation? Basically it was little more than misogynists eager to get rid of all females who were thought to be outspoken, knowledgeable (such as herbalism etc) and for having 'the curse' ...ie. just for being near someone who becomes ill or die. I guess it was easier to exterminate what didn't fit into their religious beliefs. Witches being burnt is a myth btw ... most were hanged. On a lighter note, at least Sabrina has shown us that not all witches are old!! lol