Moral prudence is a matter of philosophy and theology. I can say that it would be incredibly fiscally imprudent to legalize crack. Legalization is tolerance and tolerance leads to acceptance.
It's legal to insult your wife, and to get blind drunk in your own home. Are those acts "accepted"?
Drug use would increase and that will get expensive very quickly. In the end, you will pay sky high taxes to subsidize the drug addicts just the same way you currently subsidize millions of unwed mothers. Societal degradation is very expedite and definitely not worth a high.
You assume that a large number of people would not only use drugs but use them to the point of inability to support themselves. Why should anyone believe that? Are there that many people who are deterred from drug use by its illegality, but who would not be deterred by the risk of addiction and degradation? Is illegality YOUR sole reason for not using drugs?
Alchohol and crack are completely different animals. Members of society collectively determine which freedoms are worth their negative externalities. Our country came to the conclusion that the right to drink is work the inherent risks. We haven't concluded that crack is worth the risks.
What are the "negative externalities" of crack use that we haven't collectively determined to impose on ourselves? We have collectively determined to impose,for example, welfare costs on ourselves just as surely as we have collectively determined to ban crack.
[a tank or an antiaircraft gun or a nuclear missle] can directly harm many other people at a stroke; crack directly harms only the user.
An antiaircraft missle doesn't necessarily hurt anyone. Hey, maybe it's just for shooting empty oil barrels on his property.
That possibility doesn't negate the distinction I pointed out.