Chickenpox Parties and Varicella Zoster Virus?

Why did Chickenpox parties go out of fashion? What causes Chickenpox, is there a virus and what's the deal with the Varicella vaccine?
Source/Credit:
https://odysee.com/@drsambailey:c/chickenpox-parties-and-varicella-zoster:f

Thomas Rivers Debunks Chickenpox in 1923:
https://viroliegy.com/2022/01/14/thomas-rivers-debunks-chickenpox-in-1923/