Thanks, Jorbles.
There is another, rather significant, downside to Cutpurse, the more I think about it. He's the only role that can cause a death other than the scumfaction kill. That means that the Cutpurse using his dayvig puts us at even parity instead of odd parity - and the only way to restore parity is if scum target the Pearl Diver on the night he commutes. (As there are no other extra kills nor any other way to prevent the scums' nightkill).
Huh. I think this means that the Cutpurse dayvig, if he misses, actually costs Town a day. Consider:
1) If Cutpurse never dayvigs:
-- Day 1: 10 town, 3 scum. Assume we mislynch.
-- Day 2: 8 town, 3 scum. Assume we mislynch.
-- Day 3: 6 town, 3 scum. Assume we mislynch.
-- Day 4: 4 town, 3 scum. LYLO.
2) If Cutpurse dayvigs and hits town (assume Day 1 dayvig, though it doesn't really matter when for this exercise):
-- Day 1: 9 town, 3 scum. Assume we mislynch.
-- Day 2: 7 town, 3 scum. Assume we mislynch.
-- Day 3: 5 town, 3 scum. MYLO.
3) If Cutpurse dayvigs and hits scum (again, assume Day 1 dayvig):
-- Day 1: 10 town, 2 scum. Assume we mislynch.
-- Day 2: 8 town, 2 scum. Assume we mislynch.
-- Day 3: 6 town, 2 scum. Assume we mislynch.
-- Day 4: 4 town, 2 scum. MYLO.
If Cutpurse never fires, or if he fires and hits scum, we can mislynch three times without losing the game. If Cutpurse fires and hits town, we can only mislynch TWICE without losing the game. (Again, all of this assumes that the Pearl Diver doesn't restore parity by dodging scum's nightkill.)