They go mad because prior to the books the world was a magical scientific utopia but they discovered a source of energy that, if tapped, could theoretically allow people to do basically anything with magic along with eliminating the differences between male and female channelers (since each can only touch half the source of magic, and each half lets them do different things more easily).
Well it turns out this energy source was Not Satan, detected through a thinning in the skin of reality, which they bored through and consequently released
This led to the downfall of the utopia as Not Satan spread his influence and turned people violent and greedy, etc.
Lews Therin Telamon, The Dragon, and his 100 Companions attacked the Bore and used their magic to seal it shut. However, the contact made in doing so allowed Not Satan to connect to Saidin, the male half of the Source, and taint it with malignancy.
It's described as an oily taint on top of a pool of water, you can't dip into the pool without being exposed to the taint, and repeated exposure is essentially guaranteed to drive a channeler insane over time.
spoilers
They go mad because prior to the books the world was a magical scientific utopia but they discovered a source of energy that, if tapped, could theoretically allow people to do basically anything with magic along with eliminating the differences between male and female channelers (since each can only touch half the source of magic, and each half lets them do different things more easily).
Well it turns out this energy source was Not Satan, detected through a thinning in the skin of reality, which they bored through and consequently released
This led to the downfall of the utopia as Not Satan spread his influence and turned people violent and greedy, etc.
Lews Therin Telamon, The Dragon, and his 100 Companions attacked the Bore and used their magic to seal it shut. However, the contact made in doing so allowed Not Satan to connect to Saidin, the male half of the Source, and taint it with malignancy.
It's described as an oily taint on top of a pool of water, you can't dip into the pool without being exposed to the taint, and repeated exposure is essentially guaranteed to drive a channeler insane over time.