Well, doesn't that sound appetizing. It almost doesn't matter if the claim is true or not because, as soon as a product can be linked to imagery so unappealing as plastic than the damage is already done. This is the rare kind of reverse branding of a product, where something is linked to an idea that is unappealing, food to non-food. This of course is opposed to the normal branding where beer (or any other product) is linked to a lifestyle of being around beautiful women, which as many beer swilling basement dwellers tell me, doesn't require a lot of skepticism to disprove.
Yet, before I deal with the actual question, is margarine and Cheez Whiz really chemically close to plastic? It would be better to examine the questions premise in the first place, that being chemically close to plastic would make something less palatable or unhealthy.
The treat the unknown like what it seems to be a category of works really well for larger objects, which is what the human mind exclusively had to deal with for almost the entirety of its existence, but it doesn't work so well with the world of the very small.
Scientists, and alchemists, before them spent hours and years attempting to change lead into gold because of the differences in value between the two soft metals. Lead and Gold are separated only by a few protons in the nucleus and with modern means of knocking protons out by speeding up small particles and slamming them through a target material, lead can be turned into gold, but despite their similarities the reactions they have to the human body are completely different.
Which brings the topic back to where it started, even if Margarine and Cheez Whiz were chemically similar to plastic it wouldn't really be a problem, outside of perceived repulsion, which in the case of a food product would seem to still be a problem. So are they similar?
Well the history of margarine is far more interesting then I thought it would be, and is linked to, of all figures, Napoleon. In 1869 Napoleon offered a prize for anyone who could come up with a cheap butter substitute for the army and the poor. The french chemist Hippolyte Mege-Mouries then patented a mixture of beef tallow and skimmed milk which was good enough to claim the prize from the French government. Eventually the beef fat was switched to vegetable oils. It didn't turn up in some science experiment trying to create a new polymer, or as snopes tells me, a turkey fattener.
While Cheez Whiz is a mysterious mixture, I mean it's already unsure of itself as a cheese and I have no idea what its good at. Besides that, finding out the ins and outs of how it was made is rather difficult, and the best information I could find came from an extended obituary for Edwin Traisman, who turns out to be the inventor of the spread. He was a Kraft researcher who, "Led the team that combined cheese, emulsifiers and other ingredients into the bright yellow sauce called Cheez Whiz, a topping for corn chips, cheese steaks and hot dogs. It was introduced in 1953."
Now, Emulsion is the process of combining two liquids that normally wouldn't combine at all, think oil and water, and an emulsifier is something that stabilizes an emulsion...well that doesn't make Cheez Whiz sound any more appetizing.
Emulsion is used in the production of a wide verity of things, including creating things like paint, so it doesn't really help the case of Cheese Whiz, but this is purely guilt by association. Nothing about the processes makes something a non-food and recently cooks have been embracing the chemical side of cooking. I remember a set of cooks on Iron Chief using all sorts of contraptions and chemistry, so maybe Edwin was just ahead of his time.
Either way, the safety of eating cheese whiz or margarine has never really been in doubt, and in the world of the very small things that are similar still have very different reactions. A bear may be a bear whether it's a Grizzly in BC or a Asian Black Bear in China, but lead and gold will never be the same.
Thanks for reading,
-The Moral Skeptic