The problems are that once you legalize it, price will drop dramatically as there will be allot more supply(it's easier cheaper and safer to grow) for the demands. (and possibly also lower demands in most countries due to the fact the drug isn't illegal anymore and thus not as cool as meth or cocaine or what ever)
The whole blackmarket willl collapse and the legal market won't even come near to circulate as much money as the illegal one, for weed in Netherlands alone we are talking about billions of euros going to mostly people who really like spending money 
Thus legalization will defiantly hurt the entire consumers economy(houses, cars, boats, services, and in many cases the other illegal markets) on a scale hardly
I don't understand your argument on how it would have any effect on other industries. The price of marijuana would indeed drop but the taxes imposed by the state on both the producer and the distributor would essentially bring the price back up. Thus the price of weed per gram may go down a little but probably will stay the same. How this would have any effects on the housing market or the boat market is completely beyond me. It would be an industry just like alcohol or tobacco. The state would tax it, make sure the public knows of its dangers (like warnings on cig packets).
One thing it would have a major effect on is illegal immigration in the states. Does anyone wonder why so many mexicans try and get into the US? It's because Mexico sucks. And do you know why Mexico sucks? Because it's run by drug cartels that have more power than the government meaning two things: they are able to buy politicians and corrupt mexicos government and they are able to effectively combat mexicos military leading to huge wastes of money. Furthermore, the rampancy of Mexican gangs results in tens of thousands of deaths per year. Considering all that, wouldnt you try and hide in a dashboard to be someone's gardener in the "land of the free"
The cartels gain about 60 % of their money from illegal marijuana distribution. If it was legalized they would take this huge industry and allow it to be placed in legitimate channels. The results?
Mexican marijuana farmers would profit immensely and instead of paying gangbangers for "protection" they could sell their crop legally. This would create an enormous amount of jobs in Mexico and would take away one of the prinicple reasons mexicans leave the country: lack of jobs and lack of security.
The reduction of illegal immigration would have similar positive results in the states. More jobs and less money being wasted on unnecessary !@#$ like border patrol.
But really I don't even know what we're arguing here cause it seems like no one here is even opposed to legalization... Still, information never hurt anyone and god knows we could use less people sheepishly following government propaganda.
