There are indeed two separate issues, the first of which is simple spelling.
I admit, I cannot find a good reason for why the correct spelling of "donut"
should be enforced.
The second, more important issue is grammar. The students' inability to
distinguish between different grammatical constructions is deplorable (e.g.
verb tenses and different "levels of past"). While it can be said that
language is the product of our brains, it is also true (I postulate) that
much of how we think and analyze is also the product of language. The logic
of sentence construction is related to the same analytical reasoning we
expect of our students. By enforcing grammar, it is my hope that we are
clarifying their methods of reasoning.
Perhaps american students are at a disadvantage inasmuch as the english
language doesn't really have noun declensions, genders, or some of the other
more obvious oral cues to the underlying grammatical structures.
My personal pet peeve is ".. our result should of been..."