The 2006 estimate of 60% amounted to $8.6 billion so not sure where you got $15 billion. They would try to replace any way that they can - kidnapping, extortion, piracy, counterfeiting, increasing meth/coke volume, etc. And whether they can replace it all or not, does anyone doubt that they will certainly try? And their alternative activities will likely be occurring SOB meaning they will be pulling the cash from Mexican residents not American drug users.
Its almost 2012, amigo, so forget your outdated stats. Not that my 15 billion is accurate but we're still talking huge sums.
Now guess what? All of those crimes exist and existed before the present situation. And if you believe they can even come close to equaling the money brought in from illegal drugs, you are living in a fantasy land. So in the meantime, we should maintain the status quo? Nah, don't think so.
Legalize it all and let people take responsibility for their own actions. They did it for alcohol, they should do it for the rest.