What's interesting about this to me is the way it sort of causes you to examine why certain things are acceptable hobbies and other things aren't. This particular hobby has three notable attributes:
1. It's risky.
2. The end product doesn't seem particularly useful if we set aside the mental/physical benefits. i.e.: it's done for it's own sake.
3. It's novel.
I would argue that 1 and 2 are attributes that a great number of hobbies share. Skiing, Mountain biking, football, kayaking, woodworking, sitting in a chair and playing video games all weekend. All these things carry some very specific and often non trivial risks to health or bodily harm over time.
Of course because these hobbies aren't novel, the benefits of the hobby are well understood. Our understanding of the risks and how to mitigate them are also quite a bit more understood.
It seems to me that the real 'problem' with this tunnel digging hobby is how novel it is. Which consequently leads to a lack of knowledge about what the risks and benefits may be.
Of course it's possible the poor guy is just dealing with a mental illness.
I'd strongly add "4. It's isolating." There are no issues with "solo" hobbies, but it's definitely another axis and social hobbies def improve your sociability and relationships.
It's all a matter of context, people can learn to do this, but one would need a reason.
I've actually visited an old Victorian-era house that had "a tunnel" in the basement. It ran from the front of the basement, underground, to somewhere underneath the public street where it terminated in a half-cylinder chamber perpendicular to the tunnel. Everything was lined with bricks, solidly built. I was told it was used to store booze during prohibition but no one is really sure. Found this on youtube (https://youtu.be/nDTyz7ivgNk?t=78), that's the one.
Yes! It was actually a plot point in Better Call Saul season 4 that an engineer on a covert underground project violated OpSec by talking about it about it a bar, which prompted a ton of interest and follow up questions.
It's all in your attitude. If you are/act embarrassed about your weird characteristics, your listener will probably assume that's the right way to feel. Something similar happens if you are/act excited.
I have yet to hear of a mountain biker causing a collapse that destroys a nearby road, which someone raised as absolutely a possibility here. Less that the risks are "novel" and more that they are absolutely known in the mining industry which is why this is illegal.
To borrow a metaphor, I'd say that now we are just quibbling over price. :) Discussions about relative risk, externalities and the like are all very relevant when it comes to other hobbies as well.
It's just that most of the relevant conversations surrounding these things were had decades ago with other hobbies, and many hobbies probably wouldn't have a prayer of actually passing muster if they were new today - Full contact football being a good example.
This issue of legality that you raise is a good one though, and likely the most relevant, unless this guy is going out into the desert to do this.
Aside from the obvious personal risks of mountain biking (falling, personal injury) some usually unauthorized mountain bike trails can absolutely do damage to forests and ecosystems, based on bike traffic an erosion. I haven't heard about destroying a road, but there doesn't seem to be a very good reason to pick that as the specific line for acceptability. I don't think destroying roads is generally acceptable, but we also don't know if there's an actual risk of that happening in this case.
Mountain biking is well known for being an unwanted presence. It makes hiking trails into miserable obstacle courses. Made worse by the fact that if it's allowed at all, people will go as fast as they want, it's not like there's radar traps set up.
I'm in favor of majorly reducing all hobbies that have danger or inconvenience to others. If you can't play 110DB music in the streets at night, there's clearly a general precedent and consensus that your hobby is not anything special and has no right to be a public nuisance or environmental disaster.
1. It's risky.
2. The end product doesn't seem particularly useful if we set aside the mental/physical benefits. i.e.: it's done for it's own sake.
3. It's novel.
I would argue that 1 and 2 are attributes that a great number of hobbies share. Skiing, Mountain biking, football, kayaking, woodworking, sitting in a chair and playing video games all weekend. All these things carry some very specific and often non trivial risks to health or bodily harm over time.
Of course because these hobbies aren't novel, the benefits of the hobby are well understood. Our understanding of the risks and how to mitigate them are also quite a bit more understood.
It seems to me that the real 'problem' with this tunnel digging hobby is how novel it is. Which consequently leads to a lack of knowledge about what the risks and benefits may be.
Of course it's possible the poor guy is just dealing with a mental illness.