It isn't fair or right to accuse all communists of being homophobic. Communist who are homophobic are so for the exact same reason any other non-communist is homophobic: them being raised in a culture that promotes homophobia, a fear of what they don't understand, etc. It's perfectly right to call out communists who are prejudiced against gay people, but to suggest that all communists are homophobic is an act of hypocrisy and is also prejudiced.