1)As the OP.. let me clarify… My suggestion would involve not just a tax here and a tax there... but carefully planned edicts, one here, perhaps one there in response, with discussion able to be made IC, (such as the legion petition/debates a while back), with PCs able to effect what happens. and able to reap benefits and opposition suffering. That, I believe, would give people a sense of belonging, a sense of investment, a sense of success/failure in ways other than just being able to buy more potions than the other side.
As far as rift stuff mentioned... i -MUST- come out and defend the DMs on that.
2) Often DMs have given support to outlaw groups and still people leave because they dont like the issues of being outlaws.
For example, I had a character who at least three times tried to use rift-stuff to get groups/actions going.
A.) recruited some people, who, when they found out they couldnt use normal, cheap, healing/buffing sources OOC gave up on it, and decided to whine to get "fixed'.
Scratch that plotline. Vanish and come back another season.
B.) gathered in a half-orc tribe calling self their, 'witch who makes chief much strong'. had a pretty decent plot going involving getting redharts attacking west gate and then when forces called to defend, 8-10 or so super-rift-buffed hot-pant-teleporting 1/2 orc warriors attacking Tymoran temple.(yes,Minna, thats why Shevarra hung with you) That group fell apart, I believe because a couple key people in that, and other groups retired characters. Not due to DM stuff.
C.) a group of somewhat demented criminal elves who I had recruited to rift-power. Although I IC called it selling their souls to me in exchange for My own power, rituals n everything. Most of them quit the characters - or in one case, suicided in a rift-buff attack against some npcs (with DM supervision) because they couldn't, once again, deal with the OOC consequences of all the easy buffs and healing not being available.
In these cases, it was Players not liking the Mechanical consequences of their choices that led to Characters being quit, groups falling apart, etc.
Never, not once, due to DMs doing stuff. if anything, i can only think it was some DM guidance with PC miltia faction that kept her from execution for so long.
DMs gave plenty of support. More than was asked for. (I'm terrible for asking for aid. I just like to let things flow)
I Can't speak for other rift-groups that failed. just sheverras