This is an interesting topic and I wanted to add my 2 cents as a self-proclaimed 'connoisseur'.
On face value, (much like the rest of society who deems alcohol more acceptable), I find it interesting how being incredibly intoxicated the night before, and having a 'hang over' is decided as 'part of the fun of the sport', whilst perhaps a small micro-dose of cannabis would be considered innapropriate.
What hasn't been mentioned is the % of THC and CBD here. I believe that people with anxiety would actually BENEFIT from a few tokes (MICRODOSE, literally maybe even one puff) of a high CBD and low THC strain before caving. Obviously, this needs to come with prior experimentation on a very personal level. I would never suggest to dose something you havn't already tried out in the past. (AKA: find the right strain for you which you know will calm you down, and make you BETTER and more focused when caving, not something that will drain you out!) I'd also like to point out that you should know what you're taking, (TEST IT! is it laced? Where does it come from? Who grew it? What strain is it?) and TELL YOUR FRIENDS before going in. Also, is this a cave you're comfortable with? its best to pick somewhere you already feel comfortable with and you have done before. This is just what I'd do if I decided to smoke before going under. Legal or not, know what you're taking and the situation you're going into.
I have never done this, but I can see that with the right strain, it would be something excellent for me to do perhaps half an hour/ an hour before caving. It would probably make me a better communicator with my mates about my fears underground and make me feel genuinely better at being with the feeling of being scared.
Bringing it back to alcohol, I've found it VERY uncomfortable in the past how this is seen as 'fine'. Many cavers I've known have gone caving with less than 4 hrs of sleep and a hangover. That completely throws me and I find a sleep-deprived, hungover caver, a dangerous one.