Lol, ketamine is a wee bit more adverse to your body than a joint. Ley's just say that you are comparing a harmless weed to a cat tranquilizer.
But, most importantly, to each his/her own.
I tried weed two times when I lived here (in Canada) when I was 14-15 with no effect both times. After moving back to Venezuela, I went to Canada for summers and stuff and I always smoked weed with a friend of mine, finally getting high after like the third time. After I moved back here, I have been a bonafide pothead to this very day.
Weed has led me to many adventures. It gave me the confidence to try other, less mild psychedelics like mushrooms, MDMA, EX (yes, it's MDMA, but also speed and whatever the dealer puts in it), eventually LSD and, even more eventually, K (ketamine). On each drug I've had euphorically happy moments as well as suicidally (and what I call beyond-suicidally) crippling ones. It brought out some of the elements of my psychological make-up that had been long kept under control by pharmaceutical (prescribed) drugs.
Today, I don't take a single pill, smoke a lot of weed, get drunk every now and then, and I'm sadder than I've ever felt before. I am also more free and powerful, and I understand what makes me sad and how I can put it on the back-burner until the moment is better to deal with it. I also, having discovered the limits of my power and freedom, can make plans on how to deal with it.
So, if you don't want to take risks with your body or mind, don't do drugs (and that includes weed, though many people are able to smoke casually without using the gateway effect thing). Drugs are dangerous.
If you want to explore the limits of your mind, your freedom, your knowledge and your power, do drugs. Do them in high doses (find out before how much it takes to kill or seriously harm you, and do less than that; also, follow guidelines, like drinking water when on Ex), do them in awkward places and do them when you are afraid they might brake your mind.
Finally, if you already take medications like SSRI's or ADHD medications, why not give psychedelics a chance too? They worked for me.