@mso, well the thing about that is, with most things we understand what and how molecules decompose, what they decompose into and the temperature at which that happens. I would have to dig a bit deeper into it, but as far as I know, most flavor molecules would decompose at much higher temps than what we achieve in a pipe, and if one was to achieve those temps inside a pipe, it would no longer taste good and be beyond smokeable. It would produce acidic arid, and bitter fowl tasting compounds. and while I cant find the litature (pub chem doesnt list its decomp temp and I dont feel like looking thru my texts and databases for a forum post) I'm fairly certain there is no danger in that regard. But the concern is valid, but not for why you might think. Lots of times when things get studied they do so either by injection or ingestion, and the way ones body behaves to inhaling those things could be totally different.
Case and point, diacetyl. It's the flavor molecule that gives artificial butter (in popcorn and the like) it a buttery flavor. It's fine to eat, but inhaling it in large quantities will give you "pop corn lung". Its the chemical that has given vaping a bad rap (although all reputable US based ecig/ejuice companies removed this particular chemical from their products well over 8 years ago). Not saying all things are safe by any means. But a little research goes a long way. I'm willing to take "risks" with pipe tobacco and flavorings, and other things becuase I understand what those risks are, and I think alot of people are overly concerned about things becuase they dont fully understand them and they trust what big brother tells them and take it as absolute fact.