Most people have some narcissistic traits, particularly in competitive environments like business, politics and professional sports. I'd argue there are plenty of narcissists that don't stab people in the back, they just think they're more important than they actually are. It's "competitive" in mild form, and more delusional than manipulative in the mid range. At what point does it become a problem? "Entitled" self-obsessed people are annoying, but they aren't completely uncaring and dangerous like psychopaths are.
There's also the moral dilemna about whether narcissists, sociopaths and psychopaths really have any control over how they behave, or whether it's hard-wired in. If they have no choice, punishment achieves nothing except satisfying everyone else's desire for revenge. Is that really so much better morally than the behaviour of theirs we objected to in the first place?
I certainly think people with these behavioural patterns need treating with extreme caution, and if they ARE dangerous then they need locking up for everyone else's protection. But for the most part putting them in the right roles, or otherwise keeping them publicly hemmed-in and accountable, is often enough. Even if it is stressful - the "get everything in writing" approach.
It's a bit hypocritical to expect adjustments for ADHD, Autism, Bi-polar etc. but then throw narcissists under the bus rather than trying to channel them in the right direction and/or limit their destructive potential. Especially as Pathological Demand Avoidance, which falls in the Autism spectrum, is easily mistaken for narcissism.