But then the private variables can impact code outside of the class, and and they are no longer truly private. Imagine you are using a library and extending it

But then the private variables can impact code outside of the class, and and they are no longer truly private. Imagine you are using a library and extending it adding a few properties for usage in your app, and one patch upgrade your app breaks because the `example.tag` stops working because the library decided to add `this.tag` as a private variable. Imagine React decides to use this, and they add a private `this.internalState`, but all react components are extended from that. So now all react components can't use `this.internalState` and if the react team ever changes the name of the private variables, then it is a breaking change and can cause code to stop working. You can say "well don't do that" all you want, but a good portion of the web uses techniques like that, and breaking code because you feel they are doing it wrong doesn't make a healthy ecosystem.