The mages can educate each other (as evidenced by other, non-Andrastian cultures). And saying change takes time means little, if we're talking about a process of systematic slaughter (one annulment per 45 years) that lasted close to a thousand years. Maybe not all the mages had it bad (Vivienne is a prime example), but most wanted change. Wynne had her son taken away, Cole was starved to death, the Ferelden circle had high suicide rates, and rapes and abuse of the rite of tranquility were rampant. That's why blood magic use was so big in Kirkwall. Those people had absolutely nothing to lose, and being faced with getting turned into vegetables (who keep some awareness - those who were temporarily brought back begged to be killed), it's no wonder they would try absolutely everything to get away.
I did not mean to imply that Circles are good. For various reasons I take issue with it. And that mages in Circles rose up and rebelled at the end of DA II emphasizes your point that mages in general were fed up with the whole system around and forced onto them (I have not played DA:I yet).
I was more aiming towards pointing out that Anders uses one perspective (that of his own) and applies it to everything (like in the OP).
That does not mean he is completely wrong; mages are quickly spirited away when they are found and secluded. They can’t be heard or seen by most of the population. So Anders was right that something had to be done and stirring trouble would inevitably be part of it.
Social reform isn't something that just happens on its own, you know. It needs people to push it.
I agree with that; creating or changing something can only happen if you do something, take action. I believe that Anders was too much focused on only one angle, setting mages physically free. He did not seem to have thought of what comes next once there was a mage revolution. Like how he would built forth on the momentum he thought he would create and continue to try change attitudes.
But I still think changes take time, though Biotic Apostate makes a good point that in this case it was loooong overdue. When something that has been accepted/ignored and perhaps is part of a long history/culture, ingrained in hearts and minds, a society will resist. Just think of racism, segregation, slavery, child labor, women rights, etc. Even now some places and cultures holds on to (or attempts to change it have failed) questionable customs which has lasted for who knows how long (it does not excuse what happens until reforms start to take place though).
Putting that aside, I wonder how much being merged with Justice changed Anders throughout the years. I read the manifesto and it seems pretty reasonable and to the point. Aimed at anyone, mage or not. I find it hard to think of any other reason than uneven writing why Anders would feel justified to blow up the whole chantry (I suppose it also depends on the kind of playthrough/relationship with Anders you have..?).