I'm indeed aware of what Cassandra said. But why has it still taken, spoken about or not, 1000 years for some to break the addiction?
We don't know how many people may have tried; it may not have been any. And we don't know if people have succeeded and they've lied about it or even weren't aware of it (I can imagine exiting the order without some objections would be complicated.)
Cassandra said something about it ... Mages speaks about their suffering but not the Templars. It makes sense.
You know, she says that, but Templars' problems get a lot of air time in the games, actually. Carroll in DAO, the Templar at the door of the chantry in Denerim, the Templar who was held in Howe's dungeon, what happened to Cullen, what happened to the other templars at Kinloch, what Alistair had to say at different points, etc. And DA2 has lots more on the templars and their problems. And while technically mages can speak about their suffering, who did they speak to before the rebellion? Most of them were locked up and allowed no contact with the outside, including their own families. Cassandra's a Seeker, and while I love her, she might be a bit biased (and may have heard more of the mages' problems than anyone else because she investigated charges of abuse of mages.)
Edit: I'm not saying templars don't have problems and legitimate grievances, but I feel too much is being built on her single statement without looking at the evidence.