We all know the type. I will help you until it hurts. I will help you so hard I will kill you. Now the pathology has a name: Pathological Altruism

From Selflessness Gone Awry, and the Damage It Can Cause – NYTimes.com:

As the new book makes clear, pathological altruism is not limited to showcase acts of self-sacrifice, like donating a kidney or a part of one’s liver to a total stranger. The book is the first comprehensive treatment of the idea that when ostensibly generous “how can I help you?” behavior is taken to extremes, misapplied or stridently rhapsodized, it can become unhelpful, unproductive and even destructive.

Selflessness gone awry may play a role in a broad variety of disorders, including anorexia and animal hoarding, women who put up with abusive partners and men who abide alcoholic ones.

Because a certain degree of selfless behavior is essential to the smooth performance of any human group, selflessness run amok can crop up in political contexts. It fosters the exhilarating sensation of righteous indignation, the belief in the purity of your team and your cause and the perfidiousness of all competing teams and causes.

David Brin, a physicist and science fiction writer, argues in one chapter that sanctimony can be as physically addictive as any recreational drug, and as destabilizing. “A relentless addiction to indignation may be one of the chief drivers of obstinate dogmatism,” he writes. “It may be the ultimate propellant behind the current ‘culture war.’ ” Not to mention an epidemic of blogorrhea, newspaper-induced hypertension and the use of a hot, steeped beverage as one’s political mascot.

Interesting phenomenon. The militant do-gooder is actually a drug addict, just the drug is an endogenous opiate.