I agree Vitamin A = Vitamin A no matter the source. However, there have been reports that say 'Synthetic Vitamins' cause harm. Again, it is all heresay and I've read some reports. There is no scientific evidence to that but I do remember reading an article on it.
Read this:
http://www.helium.com/items/105747-scientists-created-synthetic-vitamins
The point is that if the 'synthetic' the form of Vitamin C can cause harm, and the 'natural' form of Vitamin C does not, then the synthetic form of Vitamin C simply is not Vitamin C. It might be something close, but if it has a different physiologic effect, it is a different molecule.
The article you posted is not only from a questionable source, it is full of pseudo science. From your MCAT studies and courses in organic chemistry, you should already realize that the article is deliberately skewing the concept of enantiomerism. They are taking a very specific concept for a very specific manufacturing process (one manufacturing process of Vitamin c) and attempting to apply that to an umbrella category (all synthetic vitamins). This tactic lacks logic and critical thought and is a concept widely used to 'pull the wool over' the eyes of the masses.
Here's an analogy:
"See!? That brown person hates America! Therefore ALL brown people hate America!" You can immediately see the ridiculousness in that statement.
The statement could easily be changed to:
"See!? Synthetic Vitamin C is bad for you! Therefore ALL synthetic vitamins are bad for you!"
Do you see the logical problem? The latter sentence is basically the summary of that article. Completely bogus.
No scientist is going to argue that the R-form of a molecule is the same as the L-form. We already know that different enantiomers are physically different molecules that have a different effect on the body. Any undergraduate science student should be able to tell you that. Look up 'nexium' for one example of where enantiomerism has had a direct impact on pharmacology.
Articles like this one need to be outed for what they really are: A poor attempt at scaring the general population who do not have knowledge of science. As future doctors, I think it is part of our duty to try and help our patients to educate themselves about medicine and science, and how to interpret the information that they read.