Earlier quoted context omitted.
That sounds like BAD validation that needs fixing, not an excuse not to do any. Some US sites still won't let me in because (a) they insist that I must have a middle name or (b) screw up the hyphen in my surname. Many sites and payroll systems assume that everyone has a surname. Never mind its character set and ordering. Even if you don't make these assumptions you don't need to accept a binary gzipped GB of zeros or…
Designing a _good_ validation system (to reliably discriminate between "good" strings and "bad" strings, including all corner cases) is really hard, error-prone, not future-proof (standards change) and might be even theoretically impossible in some cases. Some basic sanity checks are useful, of course. But it is not a good idea to use input sanitization as the only (or even main) method of injection attacks preventio…
1) That it was easy to do right: that's why we get paid.
2) That it was an excuse not to do other checks elsewhere: defence in depth is key.
Anyhow, I hope that we're really furiously agreeing.