And what about buffer overflows makes particular data inherently(!) dangerous? As in, what would be an example of data where it is impossible to make it non-dangerous by fixing the buffer overflow that it exploits?
No, that is parsing.
> sanitization or validation or conformation - you can argue how to call it and where to use it
Sanitization is "change to make acceptable", validation is "check for conformance and reject what is non-conforming". The first one is practiced by tons of developers and it's a terrible idea, the latter is what you should do. But also, the latter is never about "dangerous" input, it's only about meaningless input.