Giving a justification is seen by these people are an excuse to debate.
For another example, trying to turn down something you don't want to do:
A: "Can you come over and fix my Wi-Fi?"
B: "No, my car's in the shop"
A: "Oh, that's OK, I can give you a ride"
B: "No, I have to go get dinner"
A: "Oh, that's OK, I can feed you"
The point is not to debate. The point is that "no" or "we don't do that" is an answer in and of itself.
For another example, trying to turn down something you don't want to do:
A: "Can you come over and fix my Wi-Fi?" B: "No, my car's in the shop" A: "Oh, that's OK, I can give you a ride" B: "No, I have to go get dinner" A: "Oh, that's OK, I can feed you"
The point is not to debate. The point is that "no" or "we don't do that" is an answer in and of itself.