Before I say this, I want to be clear that I'm in no way against disclosure, or anything you said really, Redgirl. Suppliers should disclose, and people should make informed choices.
But at this point in time there is ZERO evidence that diacetyl in the amounts we vape is harmful. The lowest dose of diacetyl that has been found to be harmful is 100 times higher than the diacetyl content found in any e-juice, even straight-up butter e-juice.
There is also no evidence that diacetyl substitutes are any safer. Although, again, that may be a moot point since there is no evidence diacetyl is harmful in these concentrations in the first place.
I really think it's premature to be warning people about something that appears to be a non-issue. And until I see a study proving otherwise, there is no reason for me to wary of it.
Some good vendors are getting trashed over something that is probably harmless.