Why do so many Christians often state that Hitler was an Atheist?

For what purpose did he vindictively select the Jews above all others and called for their extermination? He never withdrew from his church and the church validated his reasoning. Hitler only opposed the traditional christian views and supported a more Pro-Aryan christian view. In any case it was his religious convictions that set all of this into motion. Any corrupt atheist leader were not motivated by an inner conviction but by greed or personal gain. Not because they were atheist. That however cannot be certain for Theist? So why do you oppose anyone's religious convictions when they form their on denomination of the religion or commit a serious act that you deem unchristian?