Oh, the hypocrisy! [sigh]
I had never heard the expression "association does not prove causation" till I started reading nutrition-centered websites, but it made perfect sense to me. Since that time, I probably see people pointing it out several times per week. I respect the concept ... and use it often myself, especially when refuting claims of silly people on Facebook. ;-)
But when I read someone stating it, and then the very next day they reel off all sorts of epidemiological observations as support for their pet notions, it really leaves a bad taste in my mouth. They bloody well know better -- there's no excuse for it.
Sometimes observational studies are the best we can hope for -- an RCT is completely impractical for some hypotheses, and totally impossible for others. We HAVE to depend on animal studies for some things, and it's a real pity to "do that" to them as well, but how else can we learn certain things? I understand that it's easier on the consciences of experimenters to torture mice than dogs, but mice make piss-poor surrogates for human subjects....
In the absence of proper human experimentation, we need to use open-minded INTELLIGENCE in choosing supportable hypotheses about what we should do concerning this-or-that problem. Do we see a pattern in rat studies which doesn't pan out in clinical experience? Then it's GARBAGE -- chuck it out and move on to a different approach. Are there clear relationships in a study among healthy young athletes which aren't seen in the aging population? Then it's not universal, and it shouldn't be promoted as such.
It would make things SO much easier if bad science were spelled out clearly in titles and headlines: "Test-tube Science Proves Spontaneous Generation" or "According to Questionnaire Recalling Food Intake of Eight Years Ago, Pineapples Cause Acne".... But no, a lot of "science" exists nowadays with the mere goal of courting future grants, not increasing the sum of human knowledge. :-( Journalists want readership, not wisdom. Brainless, money-wasting studies have to have catchy titles and positively-phrased abstracts, or their authors will have to find jobs in the real world -- trash-collecting would probably be appropriate.
Reasons why [ahem] certain blogs are not on my list --> include some writers' support for NOTIONS THEY WANT TO BELIEVE IN using "evidence" as nebulous as the claims they decry in their competitors. If X isn't allowed to use mouse studies as support, than Z isn't, either. If questionnaires aren't adequate to support hypothesis-F, then they're not allowed as proof of hypothesis-G. What's sauce for the goose is ... oh, you know.
You can't have it both ways, doc -- and you only damage your own credibility by CLAIMING to be more discriminating.