|Perl: the Markov chain saw|
Humankind's "taming" of fire has resulted in untold deaths and vast damage to buildings and land. It's also enabled us to warm and feed ourselves more effectively.
The telephone system means it's now possible to be annoyed by telemarketers almost any hour of the day. It also means you can stay in touch with friends and family at a distance and conduct business with far-flung associates.
The internal combustion engine has led to thousands upon thousands of fatalities annually, to say nothing of the impact it's had on the environment and on the geopolitical scene. It's also given individual citizens unprecedented mobility and been a powerful engine (quite literally) of trade.
Vaccines have side effects that can cripple and kill people. They also protect the vast majority of the population from contracting dreadful diseases.
Calculus and physics make it easier to build and target devastating bombs. They also enable us to (begin to) understand the universe and to build incredibly useful tools.
(Controversial:) DDT has profoundly negative effects on the environment. It is also a phenomenally effecive way of killing mosquitos and controlling malaria in poor tropical climes.
We all know that any technology can be applied to both positive and negative ends. In the case of Perl, I would certainly argue that the aggregate good to the world is vastly greater than the bad perpetrated by a few miscreants who use it to spam, hack, etc.
And by the way, while I don't want to get all political here, I think it's worth pointing out that the overfishing problem is a classic example of the tragedy of the commons...