Propylene glycol (PG) is generally recognized as safe as a food additive. PG, like ethylene glycol, an ingredient in common anti-freeze, lowers the freezing point of water making it useful as antifreeze in addition to other uses. PG is used in RV antifreeze (the pink stuff) and in airplane de-icing sprays. The fact that it melts ice should not be a concern. Many things do. Last night I sprinkled road de-icing crystals on my pork chops. That would be salt.
The LD 50 for PG (in rats) is 20,000 mg/kg. The LD 50 for ethanol (in rats) is 7,060 mg/kg, the LD 50 (in rats) for table sugar is 30,000 mg/kg and the LD 50 (in rats) for nicotine is 50 mg/kg. While toxicity in rats is not always directly translatable to humans, it generally follows that what is toxic to rats is toxic to other mammals and while the toxic doses might differ some, the trends are the same. LD 50 is a commonly used measure of acute toxicity. It is the dose that will kiil 50% of a population. Usually the test subjects are laboratory rats, though one sees results for other critters on occasion. Some object if human subjects are used for toxicity testing, though I can think of some good candidates.
So, PG is toxicity is between ethanol and common table sugar and far, far less toxic that nicotine. Nicotine is commonly found in tobacco smoke, along with hundreds of other chemical compounds, and many of those are more toxic than PG as well.
While we should pay attention to the things that we ingest, we also need to keep it in perspective. Yes, some, perhaps most, pipe tobacco contain PG. Some don't, some seem to have a lot. I prefer tobacco that is not a sticky mess (generally, less PG) but not because it is safer or less toxic. If I were worried about ingesting "toxic" chemicals, I'd not smoke and give up Scotch, and salt, and sugar and . . . And, the LD 50 for water is about 200,000 mg/kg, so maybe I can keep the Scotch and just ditch the ice cubes?
Additive versus naturally occurring does not matter as far as toxicity is concerned. The nicotine in tobacco is natural, but nicotine is considered highly toxic. Curare is natural, and very toxic. Botulinum toxin is one of the most toxic things known and is natural.
Relax. If you enjoy Molto Dolce, good for you. It likely has PG added, but PG toxicity is between that of ethanol and table sugar. The fact that it melts ice (and is relatively inexpensive) and useful in RV antifreeze and plane de-icing sprays is irrelevant.