Perhaps you have heard that Anders Breivik, the xenophobic terrorist who murdered 77 people in Norway last summer, practiced meditation. While some out there might be temped to spin this story by suggesting that what he was doing was not meditation, I'm not inclined to do so. Given the kinds of horrorshow decisions made by Buddhist practitioners over the centuries, the fact that a mass murderer used a meditation practice as a method of detachment to prepare himself to kill isn't all that surprising.
Here are a few comments from Bodhipaksa's blog:
Traditionally, meditation is only one part of the spiritual path, and it’s accompanied with an ethical code that strongly emphasizes non-harm. Stripped of this traditional context, there’s no guarantee that meditation alone will make someone a better person.
It’s also possible to practice meditation in an unbalanced way that results in an unhealthy form of emotional detachment and a kind of emotional deadening. Sangharakshita, my own teacher, has mentioned seeing some early western practitioners of the Burmese Satipatthana Method becoming very detached from their emotions and from their physical experience. This seems to have arisen from their having misunderstood the nature of the meditation practices they’d undertaken (or perhaps they had a bad teacher or teachers).
I'd go further than this. Even with the ethical framework of the Buddhist precepts, and other teachings, there is still no guarantee that someone will "a better person." That isn't to say that the ethical teachings aren't helpful. From what I have seen and experienced, they can be life changers. But there really is no guarantee. Just ask anyone who has been in a sangha devastated by severe teacher misconduct.
At the same time, a story like Breivik's does raise many of the questions that come up with the secularization of spiritual practices like meditation. In particular for me, there is the struggle people have to let go of the view that something like meditation is a cure all. That even those who enter secular programs offering meditation somehow have picked up stories about enlightened figures, or have heard about people who supposedly cured major illnesses solely through meditation practices. And in the back of their minds, they think "that could be me too!"
I actually believe that a steady meditation practice can greatly benefit a person who has a major illness, but given all the causes and conditions present, it's never the meditation alone. And even old Soto Zen dogs like Dogen, who focused on meditation practice, didn't say that meditation is the only thing needed to become enlightened.
And so, what Anders Breivik did was take a practice and do it in isolation to meet his own ends. It's possible that he even technically followed the traditional instructions for said practice. (Learning to detach from the swings of emotional disturbances is part of Buddhist practice after all.) It could be said that while there's no guarantee that someone will become a more ethical person by practicing within a complete Buddhist framework, it's unlikely that someone who is otherwise living a destructive life will pull out of that through meditation alone.