A code of conduct that is not binding but is still posted prominently in many public places would benefit the social norms without imposing a huge burden on the government. Codes of conduct, socially, make things far more efficient and cordial, and teaches people to respect the public goods and services.
We need to make sure that people understand that when they are on a mode of transportation, they are in an enclosed space for a certain period of time. This demands that they have respect for their fellow passengers and do not impinge on their space and their time and a code of conduct might make that more conscious.
The customer might always be right in stores and restaurants or else get the police called on them if they misbehave, but in a closed space where nobody can escape like a plane, train, ship or bus, a person acting loud, threatening, or otherwise obnoxious is a distraction to both passengers and staff, increasing the risk of an accident and a fight with another customer. There might be nothing that can be done at the time, but once the vehicle arrives it should definitely be appropriate to ban people who choose not to behave themselves on transportation. That's only for being deliberately and consistently disruptive. Dress, tattoos, piercing, hair and, of course, unalterable physical traits don't apply. The ability to ban shouldn't be carte blanche to start discriminating against respectful people who are just different from others.
Whether people are riding the bus or an airplane, there should always be a code of conduct that passengers should follow. A code of conduct ensures that some type of civility can be maintained among those who are using a public means of transportation. Plus it will keep everyone safe.
Planes should have basic requirements with regard to the level of a passenger's music volume, proper etiquette for getting up and down the aisle and back into the passenger's seat, and especially with regard to the transport of small children and their volume levels. No one really wants to spend 6 hours on a plane with a crying baby - especially late night or early morning flights - and it should be upon the baby's guardian to ensure that the peace of other passengers is not disturbed.