In three easy steps:

1-  Lump all Christians together into one massive Borg-ish collective.
2- When one or a tiny minority of the collective does something stupid- attribute that stupidity to all.
3- Mock the entirety of Christianity.

Like this chap has done-

So, if Christians were actually lame and unintelligent enough to adopt atheistic reasoning we could

1- Hear of some atheist or atheists who were child molesters.
2- Denounce all atheists as child molesters, since they all clearly share the same exact mentality.
3- And mock all of atheism.

Except Christians are too smart to act that way. It’s a shame that the ‘reason exalting’ atheists exemplified by the clearly angry atheist lad above in his feckless ‘tweet’ aren’t as smart.

On the other hand, it could have gone:
1- read one atheist’s twitter admonition to some Christians making threats of violence.
2- denounce all atheists as “Lump[ing] all Christians together into one massive Borg-ish collection”
3- and mock all of atheism.

Now, I know full well that not all Christians think that way.

But I know one who does.