Who actually sides with Meredith?

I'm not disparaging you, I'm arguing with you. Much more fun.

So you think the Templar leadership needed to be dealt with, but rebellion against them was wrong? It was Templar control of the city and Templar crackdowns on mages and their political enemies, that put put Kirkwall in dire straits. Rebellion against tyrants like that is justified. Waiting around for them to give up power as they subjugate or slaughter everyone opposed to them would never have worked.  

Law and order Hawke wasn't thrilled and REALLY REALLY tried to get everyone to talk out their disagreements, but when that wasn't an option, restoring order did seem like the best way to protect people.

Dealing with Meredith is a 'later' problem. Damage control is a 'now' problem.

Rioting, a potential exalted march, and trying to restore order is important. It's not the right time for idealism or a huge clash. It's time to make sure that the streets are safe.

Of course, then Meredith's sudden but inevitable betrayal happens. And then Hawke is Viscount. I like to think she tried to make Kirkwall slightly less of an insane cesspool before she took off chasing Corypheus.

We can talk about the math and Kirkwall. (Without metaknowledge)
Lets's see, what probably happen, if Hawke siding with Orsino.
Hawke know, what Orsino said: when the fight started, they all became apostate. And Hawke also know: the Exalted March coming. So: if they win: all of the mages run away from Kirkwall, and the Templars also died.

Simple math: problem solved. All dangerous thing eliminated. 

bear43

You say "Immediate threat" but I don't understand.

Meredith and Orsino was arguing about a Circle Tower Inspection. Meredith was arguing that there were blood mages to be found.
Orsino said there were no blood mages and that the search was invasive in a Circle that already had like 0 privacy considering even their letters were being read. The mages weren't allowed to leave the Gallows. Etc.

Their argument escalates a bit, and they say that they need to talk to Elthina.

Anders steps in, and blows up the Chantry.

Now. The Templars are trained and will follow orders. The local guard is trained and will follow orders. The mages are still, innocently or not, in the Gallows/Circle Tower doing what they were doing 5 minutes before. Eating. Sleeping. Studying. Taking a dump.

The PEOPLE of Kirkwall are probably mostly going, "Oh maker, my house is on fire, where are the kids? Did the Qunari come back? Are we under attack?"

NOT, "Fuck the kids and my house burning down. I'm marching with my pitchfork RIGHT NOW, getting on a BOAT to the Gallows [and if those mages who obviously did this aren't already dead], I'm killing EVERYONE THERE."

The Mages in the Circle tower also have ZERO CLUE what just happened. I mean, at worse, they'll make a break for freedom in the confusion. Not be like, "This is my time to become an abomination! Yes! Mwuahhahaha!"

If Meredith had truly been interested in "restoring order" and doing justice for the Kirkwall Citizens, she would have arrested Anders or put the sword through him right there...and worked with Aveline to save survivors, put out the flames, etc.

Then, with Anders act as evidence, requested an Annulment of the Circle.

But in that moment? As "innocent" Kirkwallians deal with fire and rubble and death, and probably opportunistic rioting bandits? NOT THE TIME TO ANNUL THE CIRCLE.

WORST TIME EVER.