Barmy, that's exactly right. Catching chickenpox for the first time as an adult is more dangerous than catching it as a child, and can often lead to serious complications including pneumonia. The scarring is much worse, as well, and the fever that comes with it is likely to be much higher, possibly dangerous in and of itself.
This is why people would willingly give it to their kids - a few days of misery and rash with a slight fever, and you're protected for life.
However, the virus stays with you for life, usually living in your nervous system. If there are times when your immune system becomes compromised for some reason - age, or great stress, or another illness - the virus manifests itself in the form of shingles, named for the horizontally striped rash that develops, usually on your sides, though it can show up in other places (it happened to my wife when she was pregnant and having gall bladder issues and still trying to work, STRESS!!).
Since some kids also develop serious complications, they went and developed a vaccine, which put an end to those pox parties. If you're an adult who's never had it, you should get vaccinated - if you don't know whether you had it, they can test for the antibodies to see if you really need it.
Disclaimer: I am not a doctor, just a Ph.D. who's had to deal with vicarious shitloads of medical issues.