Prostitution is actually a bad argument. The places where it is legal, prostitutes get things like health care, readily preventative measures against the spread of STDs and forgo the need for pimps.
The "war on drugs" is really pre-crime. Its the notion that everyone that does x becomes an addict. That everyone eventually falls down the slippery slope of needing to commit crimes like stealing to get their fix, which I think we can agree just isn't true.
As a Christian, and this sadly should not be but may be hard to believe, I follow the path of free will. You are free to destroy the planet if you so choose. Its not my right to determine which poison you wish to ingest is right or wrong for you. While I do agree that some choices do have societal consequences, a "one size fits all" approach with prohibition is complete bullshit.
I do agree that measures should be taken to protect myself from others, when my actions actually do affect them. Take DUI laws for example. There's clear evidence driving while intoxicated can lead to incredible lapses of judgment. Does it mean every time you're behind the wheel with any blood alcohol count you're gonna kill someone? No but there's a severely increased chance. Yet even then I may be able to handle a higher blood alcohol content than you, so this argument is also brittle.
I guess my main point is other countries have legalized a spectrum of substances at a much less threshold of pain than we have. Its as if they seen what a colossal waste of time, energy, and resources it produces. Yet in America we let our pride get in the way of every fucking thing. We'll continue this "war on drugs" and equally our "war on terror" until we're no longer a nation. Both have pushed us close to oblivion because consistently no one is seeing any positive results. The rest of the world recognizes our folly, repeatedly calls us out on it and what? We continue business as usual? I'm sorry, I don't wish to be labeled as that incredibly dense, stupid, moronic, retarded, juvenile, or whatever other petty words I can come up with. I think we're smarter than that but if you (and by you I mean second person you all) wish to continue this farcical charade, knock yourselves out.