There are a couple things I can see it affecting.
1) Amount of overall troops will be reduced
- delays development of 15c caps
- lot of troops will be needed to fight / defend NPCs rather than used in kingdom wars
2) Kills the 15c for defenders
- a defender can no longer get a 15c without relying on offensive kingdom members help
- defenders have enough issues as it is trying to kill hideouts, let alone adding more NPCs to attack
A different solution could be to not allow Menhir function within a certain distance of a cropper.