Alright, let's get a few misconceptions out of the way first before I move on. First, thanks to Apophis2412 for the map and information about the relative size of Thedas, that was very educational.
Second, Caridin cannot operate the Anvil. He tells you this when you meet him, golems are physically incapable of using or touching the Anvil in any way. When I first saw him make the crown I was like "lolwut?" but I'm forced to assume this was just a cinematic convenience and for all we know the Anvil of the Void can be used as an ordinary anvil as well as a demonic robot-making machine. If Caridin cannot operate the Anvil because he was made a golem, and Caridin was also the only one who was smart enough to make control rods, it logically follows that when his king made Caridin into a golem, he also inadvertently lost his only way to make golems as well. We're also told that without a control rod, golems are not just born as golems with free wills, they're made insane from the pain of their transformation and go on a killing spree. Control rods are needed to keep golems in check, and we're just forced to assume this did not happen to Caridin because of his extreme intelligence and sheer force of will. Remember, Shale lived as a mindless golem for a very, very long time and did not regain her sentience until her control rod was damaged in some battle. As a golem, Caridin wanted desperately to destroy the Anvil, but he could not, so his only option was to seal off the Anvil and build all those traps to prevent more dwarves coming to look for it and rushing to their deaths, and wait patiently for the day someone smart enough to come along and destroy the Anvil for him.
Third, Branka didn't know immediately how to use the Anvil when she got there. She just had a control rod, and was able to seize control of several golems that were already present. It's fair to assume a golem cannot use a control rod, not even Caridin. After you killed Caridin, she probably had to study the Anvil for some time before getting the golem-ization process down pat, plus she was already aided by Caridin's journal. And this is Branka we're talking about, a Paragon who is a genius engineer and inventor. It's fair to assume that only those with great mechanical expertise, or possibly even only dwarves, because we don't know the full magic of the Anvil involved, can use the Anvil. At the time, the only such being is Branka. We have no evidence to support the assumption that if we gave the Anvil to anyone else, they would be able to use it. Like I said, it's highly possible that if/when Branka dies, no one else will ever be able to operate the Anvil again. Branka doesn't seem like the type anyways to share her trade secrets.
Fourth, Orzammar is in no real danger. Paragon Aeducan led the defense of Orzammar, and as a last-ditch effort the entrance to the Deep Roads were sealed. Orzammar has been safe, and well-guarded for, for all we know, centuries. You people talk about the Darkspawn as if they're some kind of hyper-intelligent Borg that spends every waking moment trying to invade Orzammar, when really they're more dull-witted beasts that fight each other readily when no other opponent is made available. The Darkspawn do not actively bang on Orzammar's doors, they just form routine raids in the nearby Deep Roads from time to time, as such is their behavior. The real dangers of Orzammar are political stagnation, poverty, an unwillingness to change by the conservative leadership. Like I said, if the outdated caste system was dissolved and the dwarves began conscripting warriors en masse, they would not even need the aid of the golems to reclaim much of the Deep Roads.
Alright, as for the Thaig-Great Thaig thing and the distance in the Deep Roads, until we're given some sort of detailed map with distance measurements (as well as more information on the Thaigs themselves) we're gonna have to save this for another time. But like I said, there's a difference between being able to cleanse the entirety of the Roads and reclaim all the Thaigs, and simply being able to defend the Thaigs that are actually inhabitated and the neighboring Roads. I don't even believe the dwarves, even with surfacer aid, can do the former, but they might not even need surfacer or golem aid to do the latter. Nor do I believe that reclaiming all of the dwarven-made Deep Roads would eradicate the Darkspawn - if they're truly subterranean burrowing creatures, it's highly possible they have some kind of underground complex or lairs that are inaccessible by even dwarves.
Another thing about the Deep Roads is, we are told the Darkspawn breach the surface like an eruption, and this is the secret to how they can swarm so quickly in real Blights. This logically follows that entrances to the Roads can be made from the surface, and the dwarves already know how to do this - they have created entrances to their underground Thaigs, made readily available from the surface, in order to facilitate surface trade. You are making it sound as if the human armies would need to travel a great, great distance to go fight some enemy really far away, when really they could be fighting an enemy extremely close to home - just underground. And again, there'd be no need to physically guard every single mile of the Deep Roads - only the ones that are actively travelled and necessary to maintain inhabitated Thaigs.
But none of this matters. We can argue the logistics of fielding a true Darkspawn-killing army and the geographics of the Roads and the mechanics of the golems all day, but in the end none of that is important because again, there's no assurances keeping the Anvil around will do anything at all in the fight against the Darkspawn. You're not handing over the Anvil to a Grey Warden, or even someone like the Grey Wardens, who will loyally use the Anvil to serve the greater good by fighting the Darkspawn. This is not the choice given to you in the game. We can argue hypotheticals like "oh maybe one day a super-good Paragon will come along and take control of the Anvil, and form a purely volunteer golem army that patrols the entirety of the Deep Roads until the end of time!", and to that I'd just say that maybe, one day Branka will go insane and seize control of Orzammar, renaming it Brankammar, and forces all dwarves to live as slaves mining rocks and forging steel to be used to make golems, and of course all political dissidents are immediately seized and made golems, and then once she has a sizable army she goes on an unstoppable rampage against all surfacers and ends up killing everyone until all that's left on Thedas is golems.
It's an easy choice for me because one of the options is apparently "keep the Anvil around because one day it
might be used for good!". In the meantime it'll be under the control of one really crazy dwarf. No thanks, I'll find other ways to defeat evil without resorting to evil. And let's assume that everything goes perfectly and the Anvil really does annihilate all Darkspawn (again, slow-moving defensive unit, never meant to go on the warpath and track down enemies) . What terrible price have we paid? We've reduced our own kind to something like the Darkspawn - soulless and evil, bred only for war. If all we've done to win the war is become our enemy, then we might as well have lost. It's easy, as gamers, to only see the practical side of things but to me this is a moral decision.
Also,
As for the abuses in the past, they're in the past. They need not happen again if people are intelligent about it.
lolno