etymology - Why is "feminism" good but "racism" and other "-isms" bad?

Feminism is generally seen as a good thing. It means something or other about achieving equality of the sexes; of treating people of different sexes the same or as well as each other.

Racism is generally seen as a bad thing. It means something or other about not achieving equality between people of different races; of treating people of different races differently and badly.

Why is there this difference between -isms? Where did it come from?

Answer

Oxford defines the suffix -ism as

1. 
   

   denoting an action or its result: baptism exorcism

   
   

   denoting a state or quality: barbarism

   
   


2. 
   

   denoting a system, principle, or ideological movement: Anglicanism feminism hedonism

   
   

   denoting a basis for prejudice or discrimination: racism

   
   


3. denoting a peculiarity in language: colloquialism Canadianism


4. denoting a pathological condition: alcoholism

There is no inherent good or bad about these uses (except possibly the disease definition).

The source, according to ODO is

from French -isme, via Latin from Greek -ismos, -isma