Sure, in a general purpose language, like Java, or Rust, or C++ you can indeed do "basically anything you want" that's why it's called general purpose, your purpose might be to run arbitrary code you found on the Internet, so, that's a thing you can do. If you can't it's not general purpose.

In a number of applications this means you do not actually want a general purpose language which is why WUFFS makes sense.

But, even when you don't have that constraint it's reasonable to ask: How easy was it to make a thing you didn't intend, by accident ?