Riding motorcycles is dangerous. Believe it or not, in 45+ years of riding, and 38 years riding on the street, and more than a couple of dead friends, I have actually noticed that it's dangerous.
Adventure is dangerous. Life is dangerous. Swapping one risk for another - whether that other risk is hookers and blow, or being a vegan triathlete - is no guarantee you'll evade bad outcomes. Telling us that bad shit can happen if one follows a path you don't approve of is no guarantee that if you don't follow that path that you'll die blissfully in your sleep, surrounded by adoring loved ones at the ripe old age of 117.
Does a new rider going off on a long ride make a lot of sense? No, he'd be far better off never to ride at all.
This is an absurd post: There is nothing that you can do to guarantee that you can evade bad outcomes. We all die. But that doesn't mean that we don't have a sizable impact in the nature of how and when we die. Which is why the basic, common sense recommendation is to not try unusual or strenuous things right off the bat in your riding career, when you're in that risky first year period.
If you accept the risk of riding a motorcycle, acting as if there are no additional risky things you can do while riding is totally absurd. There are plenty of things that you can do to increase or decrease the risk of riding. The problem is a new rider doesn't have the experience to recognize the makings of a high risk situation, how to address that situation
before it requires skillful riding to avoid, and they don't have the skills to perform a skilled evasion either.
As a result not only are they far more likely to end up in a high risk situation, they're unlikely to have the skills and ingrained habits to get out of it safely. Being on unfamiliar roads, being far from any support (roadside angels aren't exactly a countrywide thing...

), having to deal with the mental strain of handling a motorcycle, all of those things are stuff that a rider should learn to handle on their own before they go out unsupported into the world. Learn the basics of handling a motorcycle so you can focus on the unexpected, learn to work on your bike so you can recognize what has the potential to be a ride ender, what needs to be addressed at the next stop, and what can wait for a convenient dealership or garage, make sure you can handle the mental aspects of riding for a week plus, etc. All of those things can only be handled with experience, time on the bike, and without that experience you dramatically decrease your chances of a successful trip.
And at the end of the day, I'm sure every motorcyclist would rather be riding than sitting on the side of the road waiting for a stranger to bail them out of trouble, or with an exploded bike, trying to sell it to a dealership and find a flight home, or being stuck in a hospital a thousand miles from home. The likely thing that contributes to not having those experiences is learning to ride, learning to work on your bike, and developing that skillset before you set out on the road.
I'm not trying to tell anyone here to not go out and enjoy riding across the country. I'm telling them to make sure they have a reasonable chance of completing that trip under their own power before they leave, throwing the dice and leaving it to fate is a bad idea, given that we all agree on the danger of riding. Make sure it's a freak accident that takes you out, not a mundane one you could have prevented.