They demonstrate a trumped up, faux indignation aimed at a wishful caricature of Christianity. Some folks long to be hated just to demonstrate how "righteous" they are. You're right. They don't really care about this pugilized bubblehead. He's the perfect tool to sharpen their self-manufactured loathing.
I can tell you this: Had I stumbled upon two fellows pummeling one man my sympathy would be inclined toward the one at a disadvantage, regardless of any ideologies involved. I would like to see the perpetrators caught and punished accordingly.
On the other hand, those who consider existence to be nothing more than the product of unguided forces of nature have fairly well excluded themselves from credible moral commentary. They can beat their chests for someone else who cares. For them this incident is but another example of nature taking its course.
Hoi, a fifth of pithy! A wishful charicature...but why do they wish it?