Indeed
It takes a creature of pure heart to wield it
And even still
the magic is the user’s to control

@Background Pony #2E5E
This is the main theme of the Hard Reset trilogy on FimFiction, you should check it out!

Warning: this comment aproches headcannon territory.  
It is my own head cannon that the spirit of harmony is true neutral, just as an amazing piece of music has to have some discordant harmonies in it, the harmony spirit works the same  
Nightmare moon was only banished because of improper use, one pony, no matter how perfect that pony fits the catagories, cannot have friendship with them self, it is still only one note. Note that proper use purified nightmare moon back into luna  
Discord was turned to stone because the spirit of harmony knew that force would not work on a being that is made of chaos, stripping discord of his powers would kill him, removing a note from the song, removing a bit of harmony.  
Tirek gained his powers via a mix of genetics, knowledge, and training, it would have been useless to strip him of that power, and tarterus is supposedly impenetrable. The way that he broke out was by magic dying, which is something outside even the High powers of harmony could control, for while all harmony is magic, all magic is not harmony.  
And as for sunset, I have no idea, there is no real basis for that other than she tried to use a harmony element that she didn’t represent, like how sci-twi did in friendship games, but sci-twi has a basis of channeling all the harmony elements into one person, thus causing it to be formed wrong. Sunset, plot device and the spirit of harmony is based in equestria, thus being strongest and most clear cut in a world that is brimming with magic.  
Sorry for the long comment.

Comparison:
 

 
The thingie isn’t from Metroid, I guess.

The Elements of Harmony!  
(Results may vary, but are usually for the sake of peace in Equestria.)

I completely forgot that Serene is a weird fusion!

He brings up a damn good point. What have we got? 1 x Nightmare banished, 2 x Discord petrified, 1 x Sombra vaporized (ok, so he got better), 1 x Tirek life drained, 1 x demon girl. On the plus side? Uhh… Luna purified… anything else? So that’s 6:1… ouch.
 
Stitch in Time had it right, they’re the Elements of HARMONY, not the Elements of Niceness.

Wait, Parry is possibly one of those kinds of Parasytes? Then he might not be as dangerous as thought. He’s likely matured, and can’t really take a new body part.