Except that they are so bad, they're almost completely useless. On an already marginal sacred unit.
Just cutting back the frequency would be nice. Ideally, I'd like to see them start uninjured (newly dedicated flagellants would be unlikely to have crippled themselves yet), but have a fairly small chance of developing an affliction every month. Preserving the thematic flavor, but leaving the troops useful, especially if you don't intend to keep them around for long
