It's an interesting argument, and both sides have reasonable arguments.
For legalization:
I believe that the government should never try to protect people from themselves. If someone wants to kill themselves with heroine, PCP, meth, etc, then they can go ahead and do that for all I care. I'm a super libertarian though, and believe that people should be responsible for themselves rather than living in a nanny state as we do now. And as we creep deeper into socialized medicine (which we've had for some time now), they'll only use that as further argument that we have to stop the drugs because of the burden that junkies in need of treatment put on the taxpayer.
For prohibition:
The reason they would want to try to stop those hardcore drugs is because they usually lead to crime. Pot, to me, isn't hardcore. For instance, if a stoner runs out of pot, they usually pick up an extra shift at work, save up their money and buy some more. The only withdrawal symptom from pot I've ever witnessed is general crankiness. If a fiending crackhead runs out of money, they're more likely to hold up a liquor store or mug someone due to the extremely addictive nature of the drug. The argument here is that if someone gets murdered by someone freaking out on PCP, you can't really take that back. Also, pot has no link to violence in any study, or in just about everyone's personal experiences.
Either way, it's not an easy decision for anyone to make. Do we legalize drugs that can put people into a dangerous state of psychosis, or do we simply accept that people will do these drugs anyway and try to minimize the impact of their misuse?
On responsible drug use:
The argument for legalization is usually made by those who RESPONSIBLY use drugs. If two responsible users have kids, one parent should remain reasonably sober in case of emergency or they hire a babysitter. A responsible user doesn't drive under the influence. There are always people who use drugs irresponsibly though, and they're the ones that make the news and give all drugs a bad name. I've heard way too many idiots talk about smoking pot and getting behind the wheel of a car, like it's somehow better than being drunk. I've known the same idiots to crash their cars while high, but avoid a DUI because it wasn't picked up on a breathalizer. The reason you don't see any statistics on crashes caused by people being high are because:
1. Pot smoking is much less common than drinking.
2. Blood tests aren't standard, however breathalizers are.
You shouldn't operate cars or machinery if you're too tired, let alone high, drunk or hopped up on speed. The fact that someone would be so selfish as to put others at risk because they couldn't wait to get home to get high/drunk really pissed me off, and if you are going to do it, make sure you'd be comfortable with killing someone for such a trivial reason.