To put it simply:
Yes, there are some people who call themselves feminists are are jerks or threaten people. They are an incredible minority and not what feminism was founded for or used for by most people.
GamerGate, on the other hand, was invented to harass one guy's ex under the pretext of caring about gaming journalism, while having to this date accomplished absolutely nothing in the way of uncovering corrupt journalism or changing how journalists approach video games or gaming culture. They have doxxed, harassed, and whined quite a bit though.
Jerks are jerks, but they only define a movement or philosophy if the majority or participants or founders are, y'know, jerks. And, only a jerk would think that because one jerk did something horrible, it must be okeh for others to do the same.