I think what @joelkatz and others think is going on is called a Motte-and-Bailey argument. A term is given two meanings; one innocuous and defensible, and another that is more provocative. When the doctrine is attacked, advocates lean on the more innocuous meaning, but otherwise the more provocative meaning is used. In this example, feminism might be defended as "equality among the sexes" but when the battle dies down, the meaning "preferential treatment for women" or "inferior treatment for men" would be used.

I'm not sure this is really happening much with feminism, but I can think of other examples. Religious 'faith' can have unobjectionable meanings like sticking to a consistent of moral principles over time, but also can mean uncritical acceptance of miraculous claims (healing people by laying on hands, etc). Depending who you talk to and in what circumstance, you get a different definition (or a more vague definition). The insidious thing about it is that when you have bought into an ideology, it can feel much like both definitions are identical.