This is an excellent mirror of the original post. Thinking all plastic is the same is the exact same situation as the poor guy who misunderstood his science teacher when he was told all metals can oxidize.
"Common sense" is entirely dependent on a person's knowledge and experience. It has nothing to do with sense, and insulting someone's "lack of common sense" is really just an ugly way of insulting a gap in their knowledge and experience.
We all have gaps. I'm sure a professional chef would say that I had an appalling lack of "common sense." All he would actually be saying is that I've never been to culinary school and I use a knife with all the subtlety of a gorilla when trying to dice onions. I rarely use the stovetop on anything but "keep it warm" or "give me all the heat you've got" and my wife says this is because I have no "common sense" but I say why take 5 minutes to scramble some eggs when I can get it done in 30 seconds with some nice browning for flavor.