"After our team looked for volunteers, one customer refused to leave the aircraft voluntarily and law enforcement was asked to come to the gate"
He didn't refuse to leave volunarily. He decline to volunteer. Everyone has a right to 'not' volunteer. If someone is ordered to do something without the option of declining, they are not, by definition, a volunteer.
"After our team looked for volunteers, one customer refused to leave the aircraft voluntarily and law enforcement was asked to come to the gate"
He didn't refuse to leave volunarily. He decline to volunteer. Everyone has a right to 'not' volunteer. If someone is ordered to do something without the option of declining, they are not, by definition, a volunteer.