I think it'd be a good policy to answer the question before discussing why it might be misguided. If you don't answer the question and only talk about it, you end up running in circles and not making progress.

For example:

Instead of

Is there always a problem with a concept if it can be extended to cover situations other than the most idealized ones?

I deny that this is an accurate description of Phil's concept....

It is not a description of his concept. It is a question about your grounds for dismissing his model without any explanation.

A concept that "can be extended to cover situations other than the most idealized ones" is your description of Phil's concept contained in your question

It could be

Is there always a problem with a concept if it can be extended to cover situations other than the most idealized ones?

No, of course not. I deny that this is an accurate description of Phil's concept....

Well, I think it is because of X...