[footballref]

Originally Posted by ajmc

I understand and completely agree that it makes a lot of sense and is the common practice to insure that the offended coach is aware of the details surrounding a penalty, and when necessary can guide his Captain in making a penalty decision.

However to answer you questions, directly, why you need a captain is spelled out in NF: 2-32-5c "A Captain of a team is a player designated to represent his team during (c): Penalty decisions following a foul.".
Whether an official accepts it or not is immaterial, a Captain by virtue of that designation is due the respect attributed to that position at EVERY level. Much the same, as a Referee is entitled to the respect that is attributed to his designation.

On a very practical level a Captain who has been afforded the appropriate manner of respect, can prove to be a valuable ally should an ally be needed during a contest. Providing that respect costs NOTHING and can pay huge dividend.

Where is something that says it will be automatically declined if one of the captains is not on the field? Why not automatically accept?