I think moderation is the key point here. The amounts that are present in these products pose an issue for people who are already sensitive, but if you are not then it's not a poisoning issue. In large doses, prop glycol sure would be dangerous, but in a product they are not. I don't like to see them on ingredients lists on products I have at home so prefer to source far less commercial products (I don't buy ANY lotion or hair cleaners from supermarkets, for example). Most commercial shampoos and conditioners use these chemicals. It's easy to panic and see that a dangerous product is in a cleanser, but if it WERE in there at dangerous levels we would know about it.
So, personally, I avoid them where possible, only because the other ingredients in those products concern me more than that one, and mainly for environmental reasons, but also because I'm not fixated with removing all my human oils from my body!