I think that code reviews are great and very helpful for everyone. With that being said, from time to time I've received feedback on a pull request (leading to the PR being delayed for at least as long as it takes for another round of responses from everyone involved, if not longer) that I think is so completely out of left field that I don't even know how to reply. For example:
(discussing a single-page website built with an Angular-like framework): "I think we should serve these as separate pages because otherwise users will be confused"
(discussing a C89/C99/C11 stdlib function): "I think we should avoid this for the sake of portability and re-implement it ourselves"
(discussing functionality that we need a compiler extension for): "Although we use this in multiple other places, I think we should re-implement it ourselves here for the sake of portability"
Although I don't want to establish a negative tone during code reviews, I find it very hard not to get frustrated with commentary like this, especially when the reviewer is very insistent about it (i.e. multiple rounds of debate back and forth). When I see commentary like this, I strongly suspect that the reviewer is just looking for an excuse to talk, and that he or she would find some reason to semi-randomly permute pretty much any pull request submitted. I feel like this subverts the point of the code review process and drags down the productivity of the team as a whole.
I don't know how to respond to these kinds of questions without coming off negatively, because I find it hard to believe that they are being asked in good faith (e.g. if you genuinely worry that functionality guaranteed by your language's spec isn't portable enough to use, how do you get anything done at all?). How can I reply to this sort of commentary effectively?