Don't be fooled into thinking that these organizations will go away or become less violent with legalization of any particular substance. They will smuggle anything, be it humans, illegal drugs, untaxed cigarettes, etc. Their only concerns are: will it make a profit? and how can it be transported?
They will become less violent because there will no longer be any money in that market. When was the last time there was a drive by shooting or a murder because of the trade of illegal alcohol in the US? What about cigarettes? There really isn't because there isn't enough money in it. Grey markets are by nature less violent.
How did we kill the numbers racket in the US? We legalized the lottery. People still blow their entire paycheck on the lotto, but at least the money is not going into the hands of criminals to fund other illegal activities.
Will they find something else? Probably, will it be as lucrative as the current drugs trade, probably not. People do make money smuggling cigarettes, but the amount of money to be made is very limited because of the comparatively large volume needed to make any money.
By legalizing drugs, the people who use, but don't abuse, can be left alone and we can go after the people who steal and commit crimes.
Legalizing drugs is a bad idea, securing the border on the other hand will provide significantly more benefit to most Americans.
Why do you think Meth, a drug that makes Heroin look like aspirin, became so popular in the US? We clamped down on the borders so people started making their own drugs in the US.
Some people WANT to get high and they will do what they need to do in order to do so. They will try different stuff and see what works. Who knows what they will find next, a drug that can be made from flour, toothpaste, and gasoline?
By banning drugs you are attempting to outlaw the law of supply and demand. Prohibition has not worked in the history of mankind. We need to accept that and work to minimize the damage that is caused by use of these drugs. Outlawing consensual crimes is counterproductive, doomed to failure and produces unintended consequences.
If you are convinced that legalizing is such a bad idea, then why do we not ban tobacco and alcohol? They cause far more harm than illegal drugs do. We don't because we learned our lesson with alcohol in the 1920s. Yet we seem to think that currently illegal drugs are different than alcohol. Alcohol is a mind altering substance just like cannabis is. (Guess which one causes more violence.) We have cut the use of tobacco in the US in half over the last few decades and we didn't do it by banning tobacco.
There is an organization called LEAP, "Law Enforcement Against Prohibition". Check out their media section on their website
leap.cc. Lots of detailed information there.