What you are really saying is that you think countries have very good reasons to keep people that are not well off from entering. People that are well off would/do not have the same legal outcomes, and thus your measurement of law-abiding is not reasonable.
Well, yes. As far as immigration goes, the policy of most non-US western countries is primarily merit-based or if you have money to invest in the country. If you aren't educated and productive and you're not a legitimate refugee, why should a country let you in? How does the country benefit?
Canada has a generous welfare system and social safety net that that would likely be unsustainable if it let in sufficient number of people unable to support their own benefits. Even if you hold the view that drug use ought to be a public health matter and not a criminal matter, there's a limited amount of immigration that can be sustained without overburdening these services and why let in a drug user when you can let in a doctor or engineer?
In the case of tourism, it's just about limiting risk of someone overstaying their visa.
I make well into six figures as an engineer and cannot make legitimate business trips to Canada even when the company lawyer has appealed for my entry, complete with compiling a report with ample evidence of merit. It is a naive view to think that entry is merit based when I'm being denied entry based solely on the fact that I was once a teenager that was discovered to be around weed once.
> In the case of tourism, it's just about limiting risk of someone overstaying their visa.
Then why do so many performance artists have to cancel Canadian stops when they are not allowed entry? Are they really scared a platinum artist is going to become a drain on their society? That quite obviously has nothing to do with it.