It's not faith, it's called experience. Every single one of my friends that regularly smoked weed, regardless of social or economic status, ended up using harder drugs. Despite the fact that we had a very strong culture of looking down on people using hard drugs as junkies. But sure, I have to deny my own senses, because they're not peer-reviewed and I should smoke weed by default until some scientists will tell me otherwise.

That's called anecdotes, and I have exactly the opposite experience in South Africa, England, New Zealand and Germany - maybe there's a cultural factor rather than something intrinsic to cannabis?

So, who's right now? By what process should we try to get to the bottom of this?

As a thought experiment, consider if coffee (caffeine is very much an addictive mind altering substance that can be harmful in large doses) were illegal and bought and used the same way people use cannabis. So you go to your coffee dealer, and he offers you some weed. Do you try it? Maybe. Ok, now he offers you some heroin. This is where studies should step in, but my not very meaningful belief / gut feeling is that most people will say holy crap, no thanks man, I just wanted my boring old beans and weed. This has been my experience (and that of people I know) for decades, and again I'd like to stress that that doesn't necessarily imply a great many general statements I might wish to conclude from it, no matter how "obvious" it seems to me.

I'm right, because what I'm saying is reasonable. Recreational drugs are not necessary for you to survive and thus you shouldn't risk using them if there is a possibility of them ruining your life. It's common sense.

edit: This isn't some though experiment, it's real life with real life consequences. Science might be helpful, fun and all, but I don't need a rigorous science to make my life choices and stay away from things that can potentially harm or kill me. Even if I'm basing my judgement on anecdotes. Life simply doesn't work that way and it doesn't matter if you think it's not 100% reliable.

All of the people that I know that have used hard drugs also use cannabis. The opposite is not true at all, though.

Living where weed is legal, I know dozens of people who regularly smoke weed and do no other hard drugs.

Some of them are health nuts who don't even use caffeine or alcohol. (Caffeine and alcohol are proven to cause more bodily harm than cannabis at any dosage)

With few exceptions, the entire population of weed smokers that I know have successful careers, are social, and have good family lives.

There's some anecdotes for you.