Catholicism is a cult that's persecuted true Christianity for the last 1500 years.

How do you define "True" Christianity, and what makes your version of "True" Christianity better than the many other Christian sects and religions who state that their version of Christianity is "True" and yours is false?

Again, the sins of those who claim to be Christians has nothing to do with the existence of God.

As far as I know, the God you believe in is a thought.

How about talking about how the worst killers in history are all atheists? Stalin, Mao, and Hitler. None of them were Christians.

I am personally not very well versed on Hitler but from what I read, the majority of Germans at the time were Christian and it seems like Hitler used religion in part, to get the Germans to vote for him:

In Hitler's early political statements, he attempted to express himself to the German public as a Christian.[9] In his book Mein Kampf and in public speeches prior to and in the early years of his rule, he described himself as a Christian.[10][11] Hitler and the Nazi party promoted "Positive Christianity",[12] a movement which rejected most traditional Christian doctrines such as the divinity of Jesus, as well as Jewish elements such as the Old Testament.[13][14] In one widely quoted remark, he described Jesus as an "Aryan fighter" who struggled against "the power and pretensions of the corrupt Pharisees"[15] and Jewish materialism.[16] ~ Wikipedia

I also think it's worth noting that atheism alone doesn't teach anything, it just lacks a belief in God, but @arminnavabi emphasizes the need to focus on enlightenment values and Hitler did support enlightenment values.

I will ask @arminnavabi to make a video on Enlightenment values.