What about too much data? Overflow is a concern, too. Escaping is just one solution, so I shot for the more general rule.
Buffers are not supposed to overflow with trusted data either, so again, security is subset of correctness. "Not trusting" data only prevents exploit from reaching vulnerable code, it doesn't fix the vulnerability.
Don't write web applications C? ;)
What about too much data? Overflow is a concern, too. Escaping is just one solution, so I shot for the more general rule.