So, maybe you should take a town but let it without militia and wait to see what will happen...
The problem is, PKs often come to ungarded cities because they're looking for defenseless people to kill, but people won't visit ungarded towns if they don't have to (for now, the only reason is HQ minerals and uranium, and it takes about 2 mins to dig it), and if it's too risky.
So, no "ordinary" player in Northern towns = no PK.
These towns will stay PvP battlefields for Big Factions, and it seems everybody is bored with this system.
That's why militia, even if it's bugged, unbalanced... is needed for gangs, especially the ones who want people to come back in the North, to bring more players. And because it's not possible for 2 or 3 guys (you know, no one can play 24h/24) to defend a town against a big gang, militia is necessary.
If you want action, you need to have more players. Ordinary players, who will feel a little more safer (they would know that some good guys were protecting the place), will visit ungarded towns, PKs will try to strike them (cause they would know the town is not completely safe), and protectors will stop them.
Yeah, I know it sounds a bit optimistic, but it used to work that way in Den, when we were guarding this town...