To understand my opinion on this question, and upon the question that is the subject of this question, some explanation of my own beliefs will be required. I will not put a name to my system of beliefs - what I believe and why I believe it is more important to this answer than the label that people apply to my system of beliefs.
The central core of my personal system of beliefs is that - other than my belief in myself - I am not that in which I believe, and by extension, other than themselves, no person is that in which they believe.
Next comes the belief that since I am not those external things in which I believe, an attack upon those things external to me in which I believe is not an attack upon me, and by extension, an attack upon those things external to them that others believe is not an attack upon them.
From that comes my personal belief that everything that I believe must be subject to proof, or failing that, to Occam's razor: that where many explanations exist, the simplest valid explanation is best... therefore everything that I believe is subject to change, should proof or a better explanation be presented to me.
However, the previous paragraph presents my personal belief. I live in a nation in which the freedoms of speech and religion are enshrined in law, and Stack Exchange is likewise based in another nation with similar laws. Moreover, Stack Exchange has a Code of Conduct that, in essence, states that users should be nice to one another. So, even without SE's CoC, that means that the freedom of speech gives people the right to say whatever they want, and the freedom of religion gives people the right to disregard whatever anyone else says. SE's CoC limits the freedom of speech on their sites to that which is not a personal attack upon other user
So... I understand that the answer in question could be interpreted as an attack upon Christianity, however it is not an attack against any particular Christian. While I welcome attacks upon that which I believe, I understand that others need not share that attitude.
So... my opinion on this matter is that answerers may answer as they wish, so long as no personal attacks are made and the other provisions of the CoC are not violated. Should another user's beliefs be attacked in the process, then that user may either engage and challenge that attack (respectfully, of course), reassess their own beliefs, or disengage and not participate in any discussion.
Since the answer in question does not attack any user and is not objectionable on other grounds, it may stand as-is. I would suggest to the OP that should the answer in question be offensive, that the OP should either reassess their personal beliefs to ascertain why it was offensive and if their personal beliefs are those that they truly wish to have, or alternatively disengage and simply agree to disagree.
Furthermore, since the consensus of this site's moderators appears to be that the answerer has done nothing wrong in posting that answer, further suggestions to the contrary could be interpreted as a personal attack against the answerer.