It could be a cultural or language barrier, the same phrase "why in the world would you X" has a literal Slovenian equivalent that I now however think seems to carry very different connotations. Much more surprise and much less disapproval than in English.

This phrase might have set of the conversation on the wrong foot, since later on seemingly unprovoked hostility and evasiveness may have caused me to respond by hardening up and even escalating.

It is also possible that since I have recently had irl discussions regarding marriage I may have just thrown out some arguments at Alicorn that where originality crafted for someone else. If that was the case then we both became pretty emotional in the discussion because of its relevance to our personal lives. :/