Not only, for example, are liberal and socialist not synonyms, liberalism and socialism are not monolithic constructs. One can be "liberal" and reject statist oriented economies. One can be a "socialist" and and reject notions of civil rights of individuals, the virtue of peaceful resolution of political disputes.

   It's also worth remembering that not all "communists" were/are marxists, let alone marxist-leninists or stalinists. In its original conception "communism" did not include ideas such as a dictatorship of the proletariat, a revolutionary vanguard or the need to stifle dissent by eliminating enemies of the state, etc.

  Communism once meant really just a society where wealth was collectively maintained and distributed on an egalitarian basis by the members' voluntary will. In theory it actually sounds pretty good. The problem is that systems that ignore human nature have difficulty establishing themselves through voluntary choice of the citizenry. Thus,  the need of those who put ideology above humanity began justifying the use of compulsion in often exteme fashion.

  It may be a sad reflection on humanity, but fqscism and "national socialism" are probably much easier sales than communism because such systems take into account and exploit human nature more than expect it to change.