I agree. But most changes in the language are not just mistakes that happen to get widely taken up. They usually have some sort of rational explanation, e.g. social changes (youthspeak, the cultural dominance of the USA), a desire for economy of expression (sometimes castigated as 'laziness') or a desire to express new concepts in a succinct but unambiguous way (which may be what's going on with 'humanitarian.')

The misuse of the apostrophe 's' can be explained by the fact that the current rules are silly and people don't understand them. Ideally, we would drop the apostrophe 's' altogether in forming what is in effect a genitive case. It is quite unnecessary. So not just 'its windscreen' but 'the cars windscreen.' Once the apostrophe 's' had disappeared, greengrocers would no longer be tempted to write 'onion's'.