My sentiments are with you in how cruel KFC is to chickens. However, I wonder how much the good outweighs the resentment these protests generate for managers who need to meet their quota and customers who love their chicken and see the protestors as an obstruction. These actions are already on the offense, and are not going to generate an open-mindedness in many who already have their minds made up.
If you owned a salad shop, a group of fruitarians could set up camp in front of your restaurant and protest against you for "cruelty to living plants." Essentially, people could decide anything is wrong and set up camp in front of a business to protest it. Is this effective?