Modafinil (Provigil), on the other hand, has only been around for about a decade and has had limited use. We already know about some serious side-effects of Provigil that aren't associated with caffeine (see the Wikipedia article here: http://en.wikipedia.org/wiki/Modafinil#Severe_adverse_reactions). In addition, many drugs are often found to have more serious and deadly side-effects in small numbers that are only discovered after the drug has been in use for a long time (e.g. Vioxx). In addition, Modafinil is a Schedule IV drug, but caffeine is not a controlled substance at all. There is absolutely no data of which I know that indicates Modafinil is safer than caffeine. Please share if you have such data.
But who are you to tell other people which drugs they should have a legitimate right to contain in their bodies?
The words "legitimate" and "legal" share the same root. That's the point. Someone without an FDA-approved use for these medications does NOT have a legitimate right to take them. Just because we want to doesn't mean we have the right to (although on a case-by-case basis this can be debated, and rights often change. This is what our legislative system is for.)
Let me guess: you're in favor of legalizing marijuana?