Definition of againstism in English:
againstism
noun əˈɡɛnstɪz(ə)məˈɡeɪnstɪz(ə)m
US informal The position or practice of being opposed to something, or of having an oppositional attitude in general; (habitual) opposition or criticism.
Origin
1940s. From against + -ism. Compare earlier againstness, againster.