AIDS is a metaphor for atheism.
There are many ideological infections that lay waste to civilization. Racism, anti-Semitism, Communism, Nazism and fascist ideologies, among others. Depending on one's beliefs, religions may infect societies as well. I believe that Islam is pernicious. Others would posit (and I would passionately disagree) that Catholicism or Protestantism or Judaism degrade civilizations.
The damage caused by each ideology is the direct effect, more or less, of the tenets of the ideology. The abolition of private property and civil liberties, the promotion of one race or nationality over another, the imposition by force of sectarian religious precepts are all direct corollaries of ideologies harmful to humane civic life.
Infection is a good metaphor for ideologies. Richard Dawkins' concept of religion as a meme-- "like a virus only harder to eradicate" is a prime example of such an analogy between ideology and infection.
Communism is an atheist ideology, and is the only organized form political atheism has ever taken (except for the sanguinary Cult of Reason in revolutionary France). Yet atheists insist that atheism is not an ideology, anymore than black is a color. Atheists insist that their disbelief in God isn't an ideology.
I disagree. Atheism inherently involves certain quite clear ideological assertions-- there is no transcendent purpose to existence, man is an evolved animal and not a spiritual being, there is no moral code that transcends man's mind, etc.
But there is a glimmer of truth in atheists' claim that atheism isn't an ideology. While atheism certainly has ideological consequences, it is not generally asserted as an coherent system of belief. That may be because atheists are incapable of coherence-- a view buttressed by acquaintance with New Atheist literature-- or it may be merely a propensity of atheists to anarchy.
But this iconoclastic vein in atheism raises important observations about atheism's political and social consequences.
The hallmark of totalitarianism is the concentration of power in the state. Everything for the state, nothing outside the state, nothing above the state. This differs from authoritarian rule in that authoritarian rule often leaves large concentrations of non-state power-- in churches, in civic groups, in education, in the family, etc-- relatively intact.
In the West, the most effective impediment to state power and to totalitarian rule has been the Church, in its Catholic and Protestant forms. Christianity, even when established as the state religion, has long served as a break on absolute state power. One could even make the case that much of the history of Europe from the fall of Rome to modernity has been the incessant shifts of power between church and state. The shrive of Henry IV on his knees in the snow before Pope Gregory VII is the paradigm of the moderation of state power by the Church.
Atheism destroys the check on power by removing the Church from civic life, just as theocracy destroys the state's check on power by removing secularism from civic life. The result is unchecked state power, which, in every atheist state in human history, has produced totalitarianism.
Atheism then is an infection, but not quite like religious infections. Atheism deprives the body politic of its resistance to state power. It destroys its immunity to totalitarianism, by destroying the primary alternate allegiance-- allegiance to God-- that has long served to check the state.
Ideological memes like communism or Nazism or fascism are like smallpox or tuberculosis or typhus. They are deadly, can spread precipitously and can be very hard to eradicate.
Atheism is a different kind of infection. Atheism destroys recourse to religious authority. Atheism destroys the most important check on state power-- the Church-- and leaves a civilization defenseless against the state and defenseless against a host of opportunistic ideological infections.
By driving the Church from civic life, atheism deprives the body politic of its immunity to totalitarianism. Atheism is less an infection than it is an annihilation of a civilization's defenses against totalitarian infections. Atheism is an infection that kills mainly by leaving a civilization defenseless against other infections.
Atheism is like AIDS.