Here's what I don't get-- is the opposition really arguing that there is something inherent in the nature of marijuana that, chemically speaking, makes you want to try other drugs? I cannot possibly see how any drug in its very chemical nature could have that property.

That's like saying that there is something chemically inherent in chicken meat that makes you want to eat human meat--it just ain't so!

I will concede that more people try marijuana as a gateway to the world of illegal drugs than try cocaine, but there's nothing inherent in the nature of marijuana that it must be so. That's simply a result of marijuana being popular and easy to acquire, both of which are merely societal conditions, and of marijuana being a relatively harmless, approachable drug: a good reason to legalize it, not to ban it!