You didn't really answer the question. The GP was asking, how can Rust claim to be "memory-safe" if 10% of application code (e.g. Servo) is unsafe code. We can accept unsafe code in the standard libraries (equivalent to how C# or Java or Go are implemented), as it's reasonable to assume it will be extensively peer-reviewed and battle-tested.
You shouldn't be writing unsafe application code. If your applications needs new unsafe abstractions (which you can think of as language extensions), then you can write those. But unsafe is absolutely not for application code.
(This is, as I explained downthread, part of the reason why I dislike going around quoting "X% of the code in Y app is unsafe." Your application code shouldn't be unsafe.)
