"Why do you need it?"
No one needs it. I doubt anyone will argue they
need it unless they're addicted to something that has produced withdrawl in which case they really do need it. But the problem with this kind of mentality is that it lumps all drugs in as "bad". This is part of the failure of our current prevention and education system. Telling the kids all drugs are bad leads to more use. They'll try some pot first, see nothing bad happened then figure they were told lies. Same with addictive drugs like heroin. Usually nothing goes wrong the first time (except overdose which is more rare for first timers than you'd think) so they think they've been lied to and then only later do they pay the price for their experimentation.
We need to educate people about drugs differently and the justice system needs to stop persecuting users and addicts as if they were burglars, rapists, and killers.
First, we need to put marijuana in the same class as alcohol and cigarettes. A little weed doesn't hurt anyone. Abuse of it does and that's what we need to teach. That marijuana abuse hurts you by taking you away from more important things in life. The drug itself can't really do too much damage. I'd equate it to alcohol use. A beer or two after work won't hurt you and getting drunk occasionally won't either. It's the consequences of abuse that hurt you, not the substance. There are plenty of completely functional successful people who drink beer regularly (not abusively or for escape) and the same goes for smoking a joint.
Then we need to get real with people and let them know what really happens when you use stimulants, opioids, etc. Let them know that the first time is dangerous but that the real negative effect isn't seen until later. Then educate people on the reasons why people use, help them spot the reasons in themselves, and explain the progression from curious one time use to full blown addiction. Lumping them all in as bad and evil is making this problem worse.
Then our justice system needs to provide treatment rather than punishment. The stigma attached to users is so unfair and hurts their chances for recovery. Once you take someone out of society and label them as "bad", "criminal", or "addict" they'll slip into that role and play the part.
I myself am a recovered heroin addict and on the board of the Heroin Epidemic Relief Organization. We're seeing huge progress by doing just what I described here. We're focusing on Will County, Illinois which is just outside of Chicago. We have politicians on board with us and we're doing a ton to change how drug users are treated and how drug education happens. Will County will likely become the model for the test of the country one day. We have a Drug Court program which gives those charged with certain felonies a chance to have their case dropped if they complete a minimum of one year in a treatment program that includes therapy, inpatient, outpatient rehab, then a halfway house and regular weekly, biweekly, and monhthly court appearances (as you move through the program and show progress) along with scheduled and random drug screenings. Participants are in the program for as long as they need to become sober (maximum 4 years I believe) and must attend school if they have no high school equivalency and must get a job which the court helps with. They also strongly encourage participants to attend college but not all do. Failure to complete the program means pleading guilty and being sentenced to the full term of whatever sentence you would have gotten had you not participated. (I do believe there might be a trial before that, I forgot).
We're also doing the education thing I mentioned too and it's working! Every county in Illinois is looking over at us to see how we're beating this thing. It's saving the government boatloads of money to make drug offenders productive citizens rather than letting them waste a prison cell and become burdens on the state.
I'm sorry to rant but whenever I hear someone generalizing drugs and drug users and repeat the misinformation the war on drugs has been letting loose I lose it. The point here is that not all drugs are created equal. Smoking pot should be a choice like smoking tobacco or drinking alcohol. And pretty much everything we were taught about drugs and their users is wrong.