I'm a seventeen-year-old girl who has never been intoxicated in her life, but after research on the internet, and also a bit of input from people I know, my conclusion is as follows:
TLDR: Weed not worse than alcohol, so why alcohol legal and weed not?
Marijuana comes in varying types, is grown and bred in different ways, and therefore can vary in strength.
For the stronger end of the weed spectrum, I can understand it being perhaps punishable to have, due to the increased chance of 'whiteys', where taking too much can cause nausea, paranoia, pallor, and unconsciousness, which I can see leading to accidents.
However, and especially for weaker strains of the drug, I believe putting a black spot on one's criminal record - thus lowering their chances of getting a job because of it - is retarded.
Marijuana, if taken before or during puberty, can stunt brain growth. It can also cause lung problems if used heavily and long-term - though apparently not cancer - and can be psychologically addictive. If you take too much, you have a 'whitey', the effects of which I've previously described. However, if you don't fall and hurt yourself during the whitey, 99% of the time, you recover fully. The 1% are usually those who are idiots who went waaaayyyyy too far and should probably be punished for their stupidity anyway???
Also, as far as I know, marijuana doesn't give you hangovers, or affects your driving as much as alcohol does. There are also little to no reported cases of people dying, or having unwanted pregnancies, directly due to weed. Alcohol, however, claims lives and virginities somewhat regularly.
So, purely from research and what I've gathered, as long as you don't take it before you're eighteen, and do it in moderation, you're basically fine. And when you do get high, you get giggly and relaxed and get the munchies and are generally pretty chill.
Why does this give people a criminal record just for having and using it if alcohol is legal?
Alcohol also comes in varying strengths and types. It also causes stunted brain development if taken from an early age, and can be psychologically addictive. However, whereas abuse of marijuana may simply only lead to whiteys and non-cancerous lung issues, alcohol abuse poisons your mind, your liver, your bladder, your digestive system, gives you a beer gut, and increases the risk of multiple cancers.
Also, the effects of getting drunk can be anywhere between becoming the life of the party, or an aggressive and whiney asshole, rather than the guaranteed 'pizza and guitar jam woooo haha' that weed grants (provided, again, you don't go too far and have a whitey - and even then, you just become afraid and feel ill, not potentially punch up someone or do the dirty dance with no pants without protection).
As long as you take alcohol in moderation - as with weed - none of the nasty long-term effects should pop up. But weed seems to be more forgiving if you do decide to take it a few steps too far.
So, to conclude: Weed does have its bad points, as with all drugs, recreational or not. However, considering that alcohol, which can be equally or more dangerous than marijuana, is legal, I don't see why alcohol gets special treatment.
... Sorry, that was almost a rant. I have no intentions of becoming a stoner, I swear. Just trying to contribute via informed decisions. X3