A cause usually breeds extremism...
Whether or not it helps is debatable.
The civil rights movement had proponents of extremism but MLK won with a more moderate approach. He was considered an extremist only by the more radical opposition.
I care about cruelty to animals but the ridiculous stances taken by PETA, (such as a chicken's quality of life and need for social interaction), have a negative effect on me.
I believe that Newton's laws often apply to more than physics. Every action results (and often deserves) an equal opposite reaction. In spite of this, that which seems extreme is usually a wrong action or reaction.