Does everyone remember in The Lord of Chaos the scene where Taim presents Rand with a Seal? Lews Therin starts ranting and tries to break the Seal. There is only one reason why Lews Therin would want to break them, the Seals are what cause the Taint. Lews doesn't want to committ suicide because he says several times that he deserves death but doesn't want to die. The Seals draw the Taint into Saidin like dye tablets in running water.