I think blanket concepts like this are the reason the OP is asking the question. Is someone in California who’s smoking a doob doing anything illegal? No, cannabis is legal in California. Is it immoral? Probably depends on your definition of immoral.
To me, I draw the line at basically whether it’s causing harm or disruption to anyone else. Smoking weed is only problematic in my mind if it is contributing to the illegal drug trade and all the issues involved with that, or it’s somehow grown/processed in a way that makes it unusually unsafe. If it’s legally grown in the US and processed/distributed legally and safely in states where it’s legal, then I’m 100% ok with it. Why wouldn’t I be? It’s no different at that point than legally distilled alcohol. And FWIW, I’m against moonshining for the same reasons. Same for porn too; I’m against the exploitative parts of it, but if everyone involved is consenting, not coerced, etc. and it’s just a fun way to make a buck, then why not? That isn’t harming anyone. Ditto for gambling. If someone goes to Shreveport and has a weekend in one of the casinos there, good for them if they enjoy it- it’s legal in Louisiana, and as long as they’re not hurting their family or doing anything that’s causing anyone harm, then go for it.
Most of the other things people rail against are very much a situation where they’ve been raised to believe that there is ONE straight and narrow path that is “right”, and everything else is wrong. They’re not so much against say… drag queens because they have some kind of carefully considered, well-reasoned position against them, but rather because in their minds, men dressing as women upends the “right” way of the world, and as a result, must be corrected, or at least decried. Same goes for gay people, trans people, swingers, and a whole host of others who aren’t doing anything that’s morally wrong, just that goes against a certain set of people’s concepts of how the world should be.
Finally, there’s the set of people who are against anything because it could be a problem for others, or because it’s a problem for a small number of people. I’m reminded of elementary school teachers who would often forbid the whole class from something because one or two kids couldn’t handle it. It’s that sort of thinking writ large. These folks tend to have the idea that because some small percentage of drinkers become alcoholics, or gamblers become problematic. They also usually believe that it’s necessarily a slippery slope or inevitable, so it must be banned. Lots of your anti-alcohol people fall into this category. They tend to believe that everyone will inevitably increase their consumption and become alcoholics, so they want to ban it so nobody does. Never mind the vastly more massive numbers of responsible and not-quite-so-responsible drinkers who still don’t become problem drinkers or alcoholics. Most of your “gateway drug” people fall into this category- I’ve met several people who basically have the idea that weed on its own isn’t problematic, but it’s a “gateway drug”, and people who smoke weed are going to inexorably move on to cocaine and heroin, so it must be banned. I think more likely it’s a gateway into the drug dealers who can supply you with cocaine and heroin, but there’s nothing about weed that leads to the other drugs beyond that. Which is a stupid reason to ban it.