Bad advice. Input is the boundary of your system. Always protect the boundary of your system orders of magnitude more than it’s internals. That’s like programming basics.
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.