User blog comment:Xilinoc/Ch. 545 - Blue Stripes/@comment-2211792-20130709150618/@comment-5398287-20130709153725

It's more likely that the breach is caused by the large number of Hollows being killed by the Vandenreich, since those souls are gone forever. Killing Shinigami and sending their souls to the Human World would actually stabilize it a bit.