The Tragedy of the Commons is a broader application of the Prisoner’s Dilemma (brief summary at Wikipedia). I wouldn’t call the Prisoner’s Dilemma the Root of Morality if it wasn’t for the fact that the Tragedy of the Commons is interchangeable with it, since the TotC is more common and a bigger problem.
Most laws are attempts to avert the Tragedy of the Commons. Take theft. Everyone is better off if theft is illegal. When property rights are stable people have incentive to make things, and society grows. In a world where everyone can take anything at will and there are no property rights it is nearly impossible to go beyond simple hunter-gatherer economics. Everyone is much better off. (as Paul Graham says: “the Europeans rode on the crest of a powerful new idea: allowing those who made a lot of money to keep it. Once you’re allowed to do that, people who want to get rich can do it by generating wealth instead of stealing it.”) But if a single person can avoid the restriction on taking things that “belong” to other people he gains immense personal advantage over everyone else, while still living in a rich and vibrant society! Thus it is in everyone’s personal interest to steal, while simultaneously demanding that no one else do so. The Tragedy is that if everyone does what is individually best for them, society crumbles (the Commons are destroyed) and everyone is much worse off, including the cheaters.
This is why the anti-vaxxers (people who refuse to have their children vaccinated) are morally evil. They are defecting in a TotC/Prisoner’s Dilemma situation. There are some miniscule risks to getting vaccinated. (Let me say right now that Autism is not one of them. Autism has been conclusively proven to not be linked to vaccination in any way, and the single study that claimed otherwise has been demonstrated to be maliciously fraudulent.) They are extremely rare, and as a compassionate society we’ve even set up a program to compensate and help people who are thusly injured. The fact that we can coordinate in such a manner makes me extremely happy, I didn’t realize we’d once had such a well-functioning government! Even if this program didn’t exist, the tiny risk of complications is worth the benefits. Small pox used to ravage populations, with a 20-50% mortality rate, usually leaving permanent scars, and sometimes causing blindness. Polio would kill and paralyze thousands per year just 60 years ago – people hid indoors during the summer months in fear of catching it. These have both been wiped out in the US, and other major childhood killers are held at bay, by a successful public vaccination program.
Anti-vaxxers take advantage of the fact that everyone else vaccinates their children. They live in areas with such a high vaccination rate that their children run no risk of catching the disease – it has been functionally wiped out. By doing so they avoid the risk of vaccination complications, and transfer that cost onto their neighbors. This is the very definition of an evil act. They are weakening herd immunity in their area for personal gain. They are no different from the thief who takes other’s property but expects society to continue to function as if property rights exist. If the community followed their example we would return to the Dark Ages in terms of infant mortality and public health. These people must be found and punished no less than the thief or the fraudster.
I’m not sure how long it took society to develop such strong taboos and counter-measures against theft and violence. But I hope we develop a strong defense against subtler TotC defectors much quicker than it took us to figure out slavery was bad.