I mean, to follow that analogy, yeah people absolutely should abandon their families if the families are out there actively murdering innocents.

The person saying that they're only staying to murder with their families because they care about them is not a redeeming quality, and they should definitely be held accountable and not excused for their crimes.

For the record, I consider any armed person outside their home country should be considered as a terrorist and a militia and treated as such. There is no reason someone from country A should be carrying a weapon in country B and attacking people there. This is 100 times even more valid when country B has not authorized this.