Second, THC is much more concentrated than it used to be and many people can get addicted because they need a constant supply of of THC after smoking for so long. If you disagree, then I'd like you to try to stop smoking for a year.
The claim that marijuana today is more potent than 30 years ago is false in the first place. Even if it were true all that would mean is that you don't need to smoke as much to get high. They have been using this 'more potent' bullshit since the 1980s, here we are 20 years later and people are still smoking mids and brickweed.
http://www.mapinc.org/newsnc/v05/n475/a07.html
http://www.reason.com/sullum/081304.shtml