This question quotes a critique in the question text.
It is my understanding* that this should be edited out.
Is that correct? I can't find this on meta yet.
* First comment under my question here
I'd say not to delete them outright in all cases, but certainly do so when they are an actual problem to the question, for example when the attempted or partial answer...
...makes the question a soapbox post: "I heard that WiFi causes cancer. I've researched the interwebs and I think it does. Can you disprove me?"
...limits the type of evidence in the answer in any way: "Livestrong claims that turmeric cures cancer. I've read the papers on google scholar, but I don't trust them. Is there any better evidence?"
On the other hand, I would allow them when they are...
...reasons for belief or disbelief: "I heard that WiFi causes cancer. If I put my face next to the router it gets warm, so maybe there's some truth to it. Is it true?"
...explanations of what the OP has attempted, but do not limit the evidence: "Livestrong claims that turmeric cures cancer, however I could not find any article on google scholar. Is it true?"