Reasoning:
For new players you want an easy experience for SP (at first),
while for MP you want most/all helpers disabled by default (most people, even server admins dont customize the settings)

As such its vital whats default for SP and MP.

Note:
OFP had this tech with difficultyMP.
There was also the defaultXXX tech set in CfgDifficulties.

Expected:
In Arma 3 now it takes from CfgDifficultyPresets/defaultPreset the default.
There should be a defaultMPPreset option, so one can customize it. It would only set a different default for dedicated servers (unless something is assigned via server.cfg).