An airline is a business - why would a business want to transport a passenger who has a history of criminal misconduct onboard their aircraft? The airlines have a duty to protect their employees, and a duty of care towards other passengers. They also have a rightful interest in running their services on-time and without disruption.

In the US, airlines are common carriers - which involves certain obligations like published pricing and non-discrimination - but that still allows them the right to refuse carriage on reasonable grounds. You can argue what "reasonable grounds" means, but "criminal history of violent or disruptive behavior onboard an aircraft" seems like it's probably going to suffice.