One can misuse any teaching including that of Christianity. Christianity does not lend itself as easily
to this type of abuse as Islam,es hence the preponderance of Islamic suicide bombers and terrorists.
The small cult groups you speak of are rare examples of that type of abuse. However, Jim Jones was an actual communist who preached a variation called Communalism. To eliminate communism from Jones is to miss the point. Jones is a communist role model in that he practiced class genocide on himself.
When one looks at Hitler one can see almost whatever one wants to see. Hitler left many words
that can be read all over the place. There are ample words that prove he envisioned himself as a man of the left. Much like the lunatics at God Hates Fags blames everything on Gays, Hitler is on record blaming Jews for Christianity, Bolshevism,Capitalism and I may have missed plenty more.It is a mistake to read too much into any one aspect of Hitler's life. We have various psycho experts blaming every malady under the son including various diseases, homosexuality and vegetarianism. Hitler's sexual hangups had little to do with his genocidal obsession with Jews.
Nazism, Communism, Fascism, Anarchism and Progressivism all share common roots. At the turn of the century there were misguided movements that sought to elevate man to God. Nazism was the German variation on one of these themes. Moreover, like Italian Fascism it attempted to blend Socialism with nationalism. Mussolini was an articulate Socialist who was well
aquainted with Marx. His variant did not include the racial idiocy of Nazism. The racial idiocy of Eugenics was a far left movement. In America its most notorious practitioner was Margaret Sanger who was not a Christian and wanted to reduce the numbers of Blacks and met with the KKK. Communist Dubois praised Nazism and it was viewed as a competitor on the far left and not a rightist movement.
Eugenics was part and parcel of the above mentioned groups that thought technocrats/scientists
could usher in a Utopia for the unwashed masses. Hitler was obsessed with Darwin, Nietzsche and the occult not Christianity. Moreover, Christians left converts alone. The addition of racial
foolishness was a far left addition of Darwin. Proudhon also advocated killing Jews on racial grounds independent of Christianity. This is not to say Darwinism caused the Holocaust.
The crimes against Indians in and of themselves were those of colonial powers with technological
superiority. Christianity was largely incidental but certainly a factor. However, the notion that
indigenous people have rights, slavery is wrong is also a Christian based leap forward for humanity. Many missionaries were tireless advocates for the communities they served.
You seem to underestimate communists and their ability to corrode institutions. There have been numerous examples of communists trying to pervert churches such as liberation theology, the World Council of Churches and divestment drives. The most obvious counteraction was the recent move by Anglican traditionalists in Jerusalem that was incorrectly pointed out as a solely anti -gay move. The anti gay element was prominent but it was aimed at returning to traditional theology as opposed to marx based arrogant elitism.
Communist also abuse well meaning Peace Protests for their own agendas, it is just what they do.
It is a mistake to point to eugenics as "Christian". Its opponents were Christian, but it was a leftist deformation of Darwinism. The ultimate evil is the notion that man is God or technocrats should lord over the masses. Communisms man as as God has only led to Death, Neoslavery and the worst manifestations of tryany and torture ever created by man.
Ultimately, for gays to make social progress it will have to reach out in a reasonable manner to evangelicals. It is a tactical mistake to assume this is impossible based on a series of admitedly off the wall writings of lunatics. One should not bother to try and reach out to rabid bigots. However, unlike communists one can easily find decent types to engage in polite political persuasion.