I am all in favor of legalizing Marijuana. To be honest, I've never really seen the evidence that it's more or less harmful than anything else people do. A decent number of people have used and do use it without any problems. I wouldn't use it myself. Unless you're using it while driving or otherwise harming people, I sincerely don't care. Though people are gradually getting behind legalization, it's often in spite of advocates rather than because of them.
Marijuana advocates routinely overstate benefits, ignore risks
It is true that marijuana, used in moderation, can have some health benefits.
It can help cancer patients as well as other people who have to undergo treatments that suppress their appetite. It is also true that the drug can be helpful in cases of severe epilepsy that conventional medication isn't working on. However, many marijuana legalization advocates appear to have lost the plot somewhere as they seem intent on making it seem like pot is a cure for every disease that has affected the human race.
I'm not saying that we shouldn't do further research to see what else the drug is capable of. Its been shown to help with a lot of disabilities. Parkinson's is one good example. However, trying to proclaim it will cure everything not only makes advocates look more than a little crazy, it makes people on the fence regarding marijuana even more skeptical.
Particularly when their sources are conspiracy sites that peddle things like anti-vaccination nonsense.
The other problem is that many legalization advocates pretend there are absolutely no risks. This is patently untrue. While addiction to marijuana isn't overly common, it does happen. It also raises the risk of mental illness, particularly if overused.
A joint is not a serving of broccoli and legalization groups would do a great service to themselves if they stopped acting like it is.
Marijuana advocates insult the disabled
The disabled seem like a ready-made source of support for legalization. A lot of us have had bad experiences with conventional medicine. However, if I had a dollar for every time some stoner advocated that we give up pharmaceuticals that work for us, in favor of trying marijuana, I would be extremely rich.
The thing pro-marijuana groups need to understand is that while disabled people don't like being shamed into taking medication, we don't like being shamed for it. While Western medicine is by no means perfect, a lot of these medications have actually made life possible for us. We're not overly inclined to roll the dice if what we have does the job. Shrill stoners saying that we're taking "poisons" only makes Attorney General Jeff Sessions look like he has a point.
Be honest about what you want
You know why the anti-Prohibition movement was so successful in the 30's? The people who wanted it ended were honest. They just wanted to get drunk and admitted it. They pointed out that enforcement of the law was causing a lot more harm than good.
They didn't say that alcohol would cure every disease. They didn't say that alcohol had no downsides. They didn't insult potential allies. Alcohol would probably be illegal today if every other pro-alcohol person was trying to pass off beer as a full serving of vegetables.
If you want to use pot in the privacy of your own home and you don't think it's the government's business, just say that. People would have a lot more respect for you than if you go around claiming you're trying to cure every disease known to man.