Of course, this is more likely when the distribution and sale of marijuana is in the hands of criminals as they might be said to have an interest in providing other products.

if you make it legal to the point where it is available through legal channels in the same way that alcohol is, then you remove the element where it is a cash crop for criminals.

Also, that is rather alarmist urban myth. Many people I know use it and have never moved on to anything harder or been tempted to and I would think there have been studies to back this up.

I have to agree on a few of your points as I can understand the cash crop thing and my neighbors, too, have a joint once and a while (we just avoid the backyard as the smoke from either side tends to descend and hang) and don't do anything else.

However, the key thing is responsibility when using. Just like alcohol use, there will be people who abuse. My neighbors don't go driving or doing things that could hurt/put them or others in harms way because of their possible action/inaction from being under the influence. In my opinion, I think most people cannot be trusted to realize how bad their impairment is.

Being that we here in California will be voting on this in (I think) November, we'll see how it goes. It has already been voted down before but the wording is a bit different in this one. If it passes (I somewhat doubt it though), then I would expect to see some new laws on par with how we have a blood alcohol concentration (BAC) level that considers someone under the influence enough to impair judgement.