Teaching your kids how to tend bar, including when to cut someone off, is a valuable life skill.~
My personal opinion is that to prevent party-related mishaps later in life--particularly between the ages of 18 and 22--you need to teach your kids how to party responsibly before they leave your household. Thanks to the keen foresight of federal highway funding bills, this means you will almost invariably have to break the law in order to protect your kids in the US.
An ounce of prevention is worth a pound of not having to visit the cop shop or emergency department--or both--because your kid never learned about the potential dangers of satyrs and maenads before running off and joining the bacchanalia.
In the same vein, teach them to handle a firearm. And drive in bad conditions (slippery, offroad, gravel). And cross country in harsh weather on foot (rain, snow). And negotiate transit stations.
As long as you're covering all the commonplace disasters, better include how to manage their consumer credit, how to not fall in love with a train wreck of a person, and how to behave around cops.
Upvoted you, of course it doesn't. But if we are talking about "pot candy", can you say that you just like the taste, as you can with alcohol? Never tried it, maybe you can, but now I guess that smoking pot or eating pot candy involves getting high more or less.
You can also just enjoy the actual drug effects of alcohol without getting to the point of being actually drunk. I have no experience with marijuana, but I'm sure there are different degrees there as well.
TL;DR Weed and alcohol in moderation are both fine. Alcohol in excess is far worse in the short-term.
Grandparent sounds like they might not be a drinker. Fair enough, I have no issue with that, but - as you point out - there is a whole world between being teetotal and being drunk. The stereotype (which, yes, also goes for weed) is that one swig of a drink turns you into a staggering, vomiting wreck. In actuality, the mast majority of drinking (that I have experience of, anyway) is in moderation, with a meal, and results in a pleasant relaxed feeling which is totally unlike being drunk.
Weed, actually, is different - again, IME - in that the effects aren't quite so wide-ranging. Now, I've not experimented with really strong strains/forms, nor smoked an insane amount in one sitting, but a small amount has a very pleasant effect, and - for me - a greater amount doesn't really change it that much. I prefer to smoke in moderation, have a great time, and spend as little as possible.
I have never done anything I've regretted under the influence of marijuana, nor have I injured myself, embarrassed myself in public, or woken up the next day feeling even slightly bad, let alone like I want to stay in bed for a week. Apart from the legal status (here in the UK), MJ is a far superior drug in every way.