What word should be used to describe anyone who is counter-revolutionary, that is, one who opposes a revolution?
I suppose to understand the meaning of   “反革命” ,you have to know how’s this word came out .

After OCT 1st 1949,the People Republic of China was founded,leading by Communist Party of China(CPC),and base on the situation,the civil war between CPC and Kuomintang (a major political party in the Republic of China on Taiwan) isn’t ended ,that means China still needs  revolution to unify the whole country and  CPC as legal party,anyone against CPC or revolution must be illegal

反革命 isn’t only mean to oppose revolutionary,this , but more like describe the people who betrayed the CPC and distub the way of unity China ,which means illegal at all.