The basic argument is that Christianity restrained conservatives and right wingers in the past to some degree.
Which is just the kind of laughable claim Christians make all the time.
Christians are inherently better and nicer people than non-Christians, so just think how much worse it could be if atheists were in charge. Imagine how unpleasant the Spanish Inquisition would have been, if the inquisitors had been
atheists!
If you subscribe to the premise:
Christians are inherently better and nicer people than non-Christians, then the worries expressed by the article are compelling and terrifying. If you don't, then it's a sick joke.
The Fascists want to take over, put people into camps, eliminate freedom, impose draconian rules, impose harsh punishments for anyone who deviates from their image of human perfection, and generally make everyone except the chosen few suffer - but it's going to be OK, as long as they aren't
atheists.