As always, Dean_the_Young provides excellent and insightful perspectives about these issues, something that makes me wonder why DA2 couldn't do better (it's a rethorical question, by the way).
I never realized before that the Templars have been slowly dying of success. When they do their jobs properly, nobody notices they exist outside the Circles and the Chantry. With no religious war in the horizon, they also don't have many other chances to show their power. In a way, it's the same that has been happening to the Grey Wardens. No Blight? No respect. Before DA:O, the last Blight happened before the Qunari Wars, to the point some people thought of the Qunari as a greater threat than the Darkspawn.
Hawke and company, especially the kind/diplomatic Hawke with maximum friendships for companions, is one of the most corrupt actors and forces we see in the city, while Meredith is one of the most strident anti-corruption actors in the setting.
Hawke and family head to Kirkwall with the intent of taking refuge in the corruption of the nobility, and it only gets worse from there, especially in 'let's be nice and appreciated' playthroughs. Smugglers, raiders, murderers, thieves, apostate networks: Hawke not only kills them all, Hawke is them all. Your companions only aid and abett you further: Aveline will routinely bend and break rules in yours and the party's favor, Varric is a prefessional agent of corruption, Anders runs a resistence network of sorts, Fenris is basically squating and planing an assassination of a foreign official, Merrill is secretly practicing blood magic and demonology, Isabella is a smuggler and will betray and enable slavers for a boat, and the siblings are their own can of worms. Hawke is routinely engaging or exploiting, even encouraging or relying upon, systemic corruption for personal and party advancement. Rules are for losers, not champions.
And this is all portrayed benignly and benevolently, while the force cracking down on corruption the most is regularly villified for doing so.
I think it has to do with this fascination about vigilantes that comes from before the super hero comic books, that are the ultimate case of public approved vigilantism. It also relates to the concepts of justice and law. Law is not always just, while justice is not always lawful.
In DA:O was more palatable since the Wardens were actually walking with signed contracts that allowed them to take matters into their hands, while at the same time working with the legal representatives of each faction. And if there wasn't one, there were whole quests to find one (A Paragon of Her Kind, The Landsmeet).
However, before we start praising Meredith for her lawful attitude, we have to remember one very important thing: she has the same legal standing to 'crack down on corruption' as Hawke, that is, none at all. The only difference is that Hawke is a lone wolf with some friends, while Meredith has an army. That's an appeal to force, not an appeal to law.
In fact, had Meredith not stopped the nobles from electing a new Viscount, the game heavily implies that Hawke would have been the chosen one, thus making him the true authority in Kirkwall with the right to do what he does legally, while Meredith couldn't have defended her position without admitting her lack of legitimacy.
The Last Straw actually acknowldeges it by having Meredith using the "people will demand blood" argument for the Right of Annulment, a right that has nothing to do with public opinion but public security. That was the defense of someone who has put politics over duties, and Templars aren't supposed to do that.
Just like the ME trilogy was a story disturbingly infatuated with the virtues of military authoritarianism, DA2 is a tale with an incredibly soft take on corrupt societies and turns some of the least corrupt people most opposed to the rampant and selfish corruption of Kirkwall into primary antagonists.
In a way, they seem polar opposites, don't they? However, many tyrants have used the "fight against corruption" card in order to increase their power. Mussolini and his campaign against the Mafia in Sicily comes to mind.