“No, I don't” or “No, I do not” in responding English questions

Question

Consider:

A: Do you like ice cream?
B: No, I don't.

Usually in a grammar book when you answer someone's question with negation you'll use shortened answer as in "I don't". I know you can answer with a fuller response as in "No, I don't like ice cream". But why should it be "No, I don't" rather than "No, I do not"?

This has been puzzling me for years. I think both answers are acceptable for me. Just want to know if there are any syntactical rules behind this.

Answer 1

No rules per se. "Don't" is shorter to say.

"don't" is less formal than "do not".

In written form some writers will move towards "I do not" even if they would usually use "I don't" themselves when speaking.

However, in spoken form "I do not" often implies an emphatic answer.
The "not" may be accentuated verbally - which you may write
"No, I do NOT like ice-cream"
for lack of a normal way of conveying this without extra information.

"I do not like ice-cream" she said pointedly.

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Here euphony and rhyme are probably as important as anything else.
"Don't" could have been used. :

I would not like them here or there.
I would not like them anywhere.
I do not like green eggs and ham.
I do not like them Sam I Am.