What is the reader assumed to do about an article that does not bring any proof?
The video of the missile exploding is also easy to fake, but it's an important element behind the reporting.
I routinely read the news, and I've been taught in school that critical reading involves doubting and focusing on facts, sources and proofs. No sources and verifiable proofs? No facts.
Which is why the journalist put emphasis on his sources behind the missile attack: he knows how much sources and proofs are important.
If you can fake screenshots, why not fake them, which is something that can be at least analyzed for tampering?
Even more: the author mentions X public replies, where are the links?
And how could it be otherwise? You aren't the customer. Ads, or worse, billionaire political patronage, is what pays the bills for media companies. Their authority - the blind trust people have in them - is what makes them valuable for their actual customers. They're not doing science, the last thing they want is to make it easy to check their work (although, maybe I'm too charitable to scientists too here, if they make it easier to check their work it's often the bare minimum, but I digress).
One of the original points of WikiLeaks was to make a kind of journalism where claims were easy to check from the sources. But you can see how controversial that was.
