(Warning, major comic book SPOILERS spanning sixty-odd years of - Magneto-containing - Marvel comics are to be found below... As Taylor Swift so sagely warned: "Don't say I didn't say I didn't warn ya"...)
Now, in the X-Men movies, Magneto may have alternated between 'mildly dastardly but still Ian McKellen-level awesome' and 'secretly a good, Michael Fassbender-shaped dude, but fundamentally misunderstood', but fans of X-Men comics will know that even that inconsistency pales in comparison to the master of magnetism's tendency to switch sides in his comic book form.
Whether it's leading the X-Men (which he's periodically done), threatening to destroy the Earth (almost every year), creating his mutant cult (it's happened more often than you'd think) or even straight-up rage-murdering people (again, more often than you'd think from the movies), Magneto is nothing if not magnificently inconsistent.
Which, in practice, means that...
Magneto Has Done Some Pretty Awful Stuff Over the Years
Here are seven of his darkest moments...
7. He Turned His Children into Terrorists
Now, Quicksilver and Scarlet Witch may have since been ret-conned into not being Magneto's kids (or even mutants at all), but back in the 1960s, Magneto very much didn't know that.
Which means that when he basically forced the pair to join his mutant terrorist organization (subtly called the Brotherhood of Evil Mutants), he knew full well that he was being a seriously crappy parent.
6. Also, HE'S Very Much a Terrorist
It's easy to forget in the context of the decades of far more subtly drawn characterization that followed, but in Magneto's early appearances (all the way into the 1980s) he was basically exactly the sort of blindly lethal terrorist that our society tends to invade countries to get rid of.
If he wasn't threatening to blow up a city, or destabilizing the Earth's magnetic field, thus causing volcanoes to actually destroy a city...
...then there's a good chance he was battling superheroes in the streets, while calling for the violent overthrow of various national governments.
He's not exactly the A-Team, is the point...
Speaking of which:
5. He's Happy to Torture People to Achieve His Aims
Y'see, Magneto isn't just willing to blow up cities to get what he wants - he'll happily kill or violently torture people if it gets him closer to his goals (or gets him a measure of revenge)...
...like, for instance, that time where he kidnapped the X-Men, and trapped them in a state of permanent infancy:
4. He Once Literally Ripped Wolverine Apart
Now, in fairness, ripping the Adamantium from Wolverine's system - as he did back in 1993's Fatal Attractions storyline - was part of a pretty messy situation, in which Wolverine and the rest of the X-Men seemed pretty much hell-bent on killing Magneto...who was himself threatening to destroy the Earth, but even so...
Not cool, Erik. Not cool at all...
3. He Killed a Whole Submarine's Worth of Russians
Yup, that's right - Magneto once (back in Uncanny X-Men # 150) sank an entire submarine's worth of Russian sailors, and then left them to drown.
Now, that was technically a response to the Russian government attacking him, but since that was a result of him insisting that the entire planet hand over political control to him, you can kind of see why the Soviet's trigger fingers would've gotten a little itchy.
Also, just to be clear, those submariners didn't get rescued - something for which Magneto was later brought to trial for at the World Court, which prompted his first major switch to superheroism.
Though that did very little to halt the fact that (a while later):
2. He Became Everything He'd Ever Hated
Now, you could argue that Magneto - who had survived the Holocaust, and sworn to never allow anything like it to happen again - had actually betrayed a whole lot of his principles the moment he became an authoritarian dictator (a couple of times), or murdered innocents to achieve his own goals, but nothing quite measured up to the time (back in 2004's Planet X storyline) he took over New York, and basically started enacting his very own genocide...
Now, sure, it was quickly ret-conned that the guy who did all of that wasn't technically Magneto - but seeing as writer Grant Morrison had very much intended for it to be (and the later change was something of a cop out), this one can definitely be considered to still count...
And yet, it still wasn't quite as bad as that time where...
1. He Killed Pretty Much Everyone
Which, as seems to now be traditional in these articles, means that arguably the darkest moment of Magneto's career happened in...you guessed it...the Ultimate Universe.
Where (during 2008's Ultimatum event) he managed to kill millions of people (and half of the world's superheroes) with the one-two punch of a giant tidal wave and a whole lot of suicide bombers.
And, of course, a little one-on-one bloody murder (that'd below'd be Wolverine, for instance, being horribly torn apart):
Which tells us one vitally important thing: no matter how much of an asshole a character is - they'll always be even worse in the Ultimate comics...