Yet ,another example of misunderstanding and misinterpretation. There is no scope for the use of “the" instead of “a" in the question. The word teacher has been and needs to be used in the generic sense, and that is how it is used.
Your response here demands 'Discussion' on two essential and interesting topics; the Discussions stand initiated.
It will suffice to record here that:
1. It is not “a" alone which denotes the generic use of the noun it precedes. The generic use is also denoted by “the" and “plural nouns". Here are the self explanatory examples quoted from ' living authorities on English Grammar' :
“1. The tiger has no mane.
2. A tiger has no mane.
3. Tigers have no manes.
Here the tiger indicates tigers in general, not one individual (tiger).Thus [1] expresses essentially the same meaning as [2] and [3]."
Thus your incorrect generalisation that “In English the article "a" denotes a generic interpretation of the noun it precedes" does not hold ground.
2. A teacher never suffers misconceptions about oneself or others. Having full faith in the fallibility of the human race, I make and am likely to make mistakes as a teacher. However, there has been no mistake in framing the question “Who is a teacher?" . Even if there had been one that would earn a grammatical correction and not an ill- conceived 'disproportionate value judgement' not befitting an open forum.
Speaking philosophically, it is a travesty to think and believe that “the most valued person is the one with the better question, not the one with all the answers."
To deserve the tags 'good, better or the best' both the question and the answer(s) must be semantically appropriate and methodically expressed. I will refer you to Dialogues of Plato so as to get the feel of 'What a discussion should be like?'.
2. It is never a matter between 'you and me' where one will stand more valued and the other less valued. It is always between 'ignorance' and 'knowledge'.
4. Last but not the least, in the discussion about 'Future Tense' you had on the wrong side ,that did not make you less valued, not at least in my estimation.
It is a pleasure to find you getting actively involved in matters pertaining to grammar,that too, after the initial reluctance to touch grammar.
Congrats for referring to “the old Greek philosophers day" after interpreting my first post as a philosophical You are there with philosophical
Dramatic Aside:
The “Grapes (of English Grammar) are not sour (now)".