He cannot claim to reform Tevinter without abolishing slavery. And these reforms must start with him, yet I've heard nothing about him freeing the slaves he inherited after his father.
Freeing slaves in the middle of a war with a divided government would not be the smartest idea. I actually made a post which goes a bit deeper into why I think it wouldn't be wise at this point in time.
The more I hear about Tevinter's problems the more I think that it's fall is inevitable. They just have too many factors that remind me of when the Roman Empire fell.
Too many invasions
Overly reliant on slave labor
Government corruption
Political instability and infighting
Not that I don't believe in Dorian and his group but that I think it may be far too late for them to do anything about it. If they freed the slaves, how many would become citizens? Would making them citizens be a good thing? Or cause the people of Tevinter to be further divided? Will the country be able to financially support former slaves? With the loss of slave Labor, how many citizens would be able to financially support themselves? If citizens can't financially support themselves, then how many will seek financial stability elsewhere causing a population decline. Which is another factor in Rome's collapse.
Dorian's group could very well end up furthering the internal division and weakness of the country which will hasten Tevinter's end more than save it.
The fall of Tevinter may not be the worse thing in the world, it's the oldest country in Thedas so it's time is simply at an end.
But if Dorian really wants to save Tevinter then he's going to have to play dirty and perhaps make some very brutal decisions. He may have to forgive the men who murdered his father and work with them, Convince the other Magisters that they need to go on the offense with the Qunari... Or create a disease and infect the Qunari with, sort of like a Genophage.
Dangle freedom on a stick to the slaves by ending slavery officially, but not unofficially (ie Sharecropping).
In other words they have to get the slaves invested in the well being of the country while still maintaining their slave labor to prevent a rebellion , create a united government while working toward severely weakening the Qunari threat once and for all.
But that may still not be enough.