One of the most common arguments made by theists against atheism is that atheism inevitably leads to communist style dystopias where all commonly good moral values are eroded away and replaced with one person's vision of madness. They point to the horrible social experiments of the 20th century in the Soviet Union, China, Cambodia and Vietnam where religion was eradicated and millions ended up being murdered and forced into labor under the direction of the State. There is this ongoing conflation of atheism with communism that each of their existences necessarily requires the other as if they're two in the same. While it is true that communism requires atheism, atheism itself implies no political connotations at all whatsoever. And atheist can be capitalist, or a Marxist, or a libertarian, or be completely apolitical. All atheism itself implies is the disbelief in any gods.
Atheists will probably never be able to clean the dark stain of communism off of its history. But it is worthwhile to note that even if we successfully educate the masses that atheism doesn't equal communism, we are still in a position to have to explain the failed communist experiments. I agree with all the critics that the communist regimes of the 20th century were absolutely horrific crimes against humanity. I'm a critic of communism both in theory and in practice. In theory, the idea that society should be controlled and centrally planned so that individuality isn't recognized and people are turned into nothing more than worker bees and forced to build the State's vision of what a civilization should look like, is like as Bill Maher recently said, trying to make the river flow upstream: It goes against our natural need to be recognized as individuals and to be able to pursuit our own goals and happiness. Communism can only really work on small scales and when it is completely voluntary.
It is also important to note that although communism is atheistic and suppresses religious freedom, communism is not done strictly in the name of atheism. The primary goal of communism is not to eradicate religion, the goal is the establishment of the common ownership of property and the means of production for the State. From the perspective of communism, religion was seen merely as an inconvenient obstacle in the way of achieving this dream that had to be taken out.
The main problem of communism is that it is totalitarian - it allows one person to have total power. Total and absolute power, as they say, corrupts its individuals absolutely, that's why monarchies have waned and democracy is on the rise. Most people recognize that power must have checks and balances to ensure that the power is shared amongst different minds. Without this, the citizens of a communist republic are at the mercy of one person's will, and if that person is psychopathic, like Stalin was, unmitigated cruelty is almost inevitable.
Christopher Hitchens argued that when Stalin took the reigns, he was merely exploiting a vacuum of power left over by the Czars of Russia who for centuries were regarded by the Russian people as being somewhere between human and god, and who conditioned the people to credulously obey their authority without question. In other words, according to Hitchens, religious thinking and unquestionable obedience to authority enables dictators like Stalin to come to power, and that the main culprit in all of this is the willingness itself to submit to authority. I think on that he makes an excellent point.
Not that the numbers of the massacred are the most important thing to focus on, but religion itself has been the cause of much unnecessary killing and suffering specifically done in its name. Now I agree with many others that the social consequences of a belief say nothing about whether that belief is true of not, but I am also not ignorant to the role that the ugly stain of communism has on atheism. Thus, the primary reason why the word atheism in the West has had such negative connotations, is because of its association with communism, and to a lesser extent with Darwinism. In the future, as atheism becomes more closely associated with secular humanism and secular democracy, which by all measures represents a more humane and tolerant system of ethics and government, the word atheism or atheist will no longer arouse such fears as it used to.