"Very plausible" carries different connotations to "plausible". The former suggests (to me) that it really might be the right explanation, whereas the latter just sounds like it is an explanation that fits currently known facts.
Smoking has declined by at least half in the last fifty years in the United States. Also not a small effect!
"Very plausible" here means "someone should really do a study where they correlate for lower levels of nicotine use and see if there's anything left to explain".
I can't imagine anyone would see "very plausible" and think the explanation should be accepted without investigation. That's just not what that phrase means.
> Smoking has ...
Neither I, nor anyone in this thread, has contested the existence of evidence to support this claim.
> "Very plausible" here means ...
Why does "plausible" not suffice?
> I can't imagine anyone would see "very plausible" and think the explanation should be accepted without investigation. That's just not what that phrase means.
I didn't suggest otherwise.