Unless or until tobacco manufacturers are compelled by law to disclose ingredients
They are, just not in the US. The German govt has a nifty database where you can look up the additives in your favorite German-manufactured blends.
This link takes you, for example, to the contents of McConnell Scottish Flake (which I happen to be smoking at the moment). Yum, PG! And gum arabic too! The database is pretty intuitive even if you don't know German (I don't). Unfortunately for us, they're a little vague on flavorings. There's also an earlier list from 2004 that gives fuller disclosure. Just Google "Liste der Zusatzsstoffe in Tabakprodukten 2004: Pfeifentabak" for the full pdf. Here are some of the goodies contained, for example, in 50 g. of early-2000s Royal Yacht, just in case you were wondering:
WASSER 7732-18-5
1,2-PROPYLENGLYKOL 57-55-6
ETHANOL 64-17-5
KALIUMSORBAT 590-00-1
ETHYLACETAT 141-78-6
AROMA verschiedene
I don't understand the numbers, but if it's got trace amounts of ethanol, I'm in!
Personally, I could give a shit about what's "natural" or not when it comes to tobacco. They could list "mechanically-separated baby Koala bear" or "nuclear cyanide" in the ingredients list for, say, Telegraph Hill, and I'd still smoke it with pleasure. But it's super fun to dork out on the poisons added to our chosen poison after it's been fumigated and fertilized in the field with god knows what. That's what makes it yummy, right?