@IceKitsune  
I would agree if the wording the this panel was not so specific: “it’s one thing to use magic…”. Sounds like magic in general is not to be used against non magical citizens.  
I won’t try to look too deeply into what is said in this comic (non canon anyway), but I do have to agree with others that say that it’s a really bad excuse to nerf Twilight. Doesn’t stick with the rest of the comics or show, and raises too many questions.  
Also really stupid when you consider all the superman comparisons.

I suppose Twilight doesn’t care about animal rights, then?

Or maybe this is the sort of inconsistency you get when you have multiple writers working on different issues of the same comic without actually coordinating with each other.

@Joshua  
Are you blind and not seeing the obvious contradiction in the pic?

@armadiloeater
 
‘Superman, won’t you stop those criminals robbing the bank?’  
‘I’m sorry, but it’s unfair for me to do something, since I am immune to bullets, can fly, super strong, etc. Call Batman.’

@Background Pony #0627  
@armadiloeater  
We have no idea of what Equestrian Law is like. For all we know any use of magic by a princess of Equestria to apprehend a criminal is considered illegal.
 
The reason also doesn’t have to be excessive force it could be some other kind of law for another reason. I just used that as an example.

@IceKitsune  
Remember that she could just levitate them in the air… Or teleport them to jail, or any other means of stopping them without zapping them with lazers.  
With that out, the only thing left is: she doesn’t want to use magic because they can’t use magic, like it’s not fair or something.  
Affirmative laws for non magical Equestrians?  
Aaaah, politics in MLP do not want do not want!

@IceKitsune
 
Is it excessive force when Superman puts criminals in jail?
 
Besides she doesn’t even need to actually ‘wound them’. She knows hold and levitation spells. Hold them down, sheriff cuffs them, throw into jail, done.

@armadiloeater
 
Shouldn’t the princess be more worried with seeing lawful citizens being robbed by outlaws?
 
I don’t know, I think someone of her position should have some duty to protect her followers.

@armadiloeater  
As I said on another comment I think its more like in this case it would be considered excessive force (or something to that effect) and so they couldn’t be arrested and would just get off easily. Therefore start doing it again leaving everyone in the same place.
 
Its the only real explanation that isn’t stupid.

CONFIRMED. EARTH PONIES ARE MONSTERS NOT LIVING THINKING BEINGS. They must be put back in their place by the glorious Unicorn master race.

I think this is more about the fact that they are non magical members of Equestria, so Twilight doesn’t want to make it seem like unicorns can bully those types of citizens because they are more powerful?  
But that means that racism (or speciesism) is a concept that exists in the Equestria… Nope, does not compute.

@Ms. Harshwhinny  
And Cattle Rustlers aren’t criminals?

@IceKitsune  
And don’t pirates technically have no rights since they’re outlaws and criminals by definition?  
Mind you, I guess the bulls are outlaws too though huh? Hmm.

@IceKitsune
 

 
I don’t think you want to go this way.

Well she did say that she wouldn’t use magic against a citizen of Equestria. Are we sure that the pirates are citizens? Were they even in Equestria for that arc, I actually forget.

Coherence, what’s that?

sigh I really, really wanted to like this issue, and I really, really wanted to give Katie Cook another chance.
 
When will I learn to stop hoping for nice things…

ya know, Superman stops muggers and people say he’s a pretty good guy  
what is your excuse?

Stupid whiners thinking this comic has bad writing. When will you guys ever learn?

They’re off-limits of Equestrian justice.