The following quote is a message from an X-Men chatroom. No edits have been made to the original text beside to correct grammar and punctuation.

"It’s time to face facts: Charles Xavier's liberalism does nothing for the mutant cause.
If you didn’t know about their powers, Charles Xavier and Erik Lehnsherr would look like a pair of distinguished elder gentlemen. The difference between the two is that for as long as he’s been in the public eye, Erik Lehnsherr has always explicitly identified himself as the mutant Magneto, while for years, Professor Xavier put on the facade of being a “normal” flatscan* scientist."

*flatscan: a term used by mutants to describe non-mutants. Can be considered an insult.

"But it doesn’t end there: as leader of The Brotherhood, Magneto never required his allies to wear masks or hide who they were. meanwhile, Professor X almost always appears in public with only the most attractive (by conventional flatscan standards) of his students. He even goes as far as providing holographic image inducers for his less “palatable” students.
What all this tells us is that Charles Xavier only cares about you if your powers and appearance wouldn’t cause a stir at the country club, while Magneto fights for the rights of all mutants.
Now, more than ever: Magneto was right."

This is a blatant oversimplification, and just plain wrong in most parts.

Magneto is a radical. He is a terrorist. Whether or not you agree with him doesn’t change the fact that he KILLS people. Magneto’s goals do not require him to have a public image other than Magneto. Professor X runs a school; a sanctuary for mutant children, and teens, and adults. He requires a certain amount of social capital in order to run this school, in order to convince the parents of closeted mutant teens to allow their kids to come there. He SAVES CHILDREN'S LIVES while still allowing them to retain contact with their families and outside society. Magneto is HATED. That’s why he can walk around with an entourage of people who look like they do. That’s why he can wear a cape and a helmet and bright red everything. People look at him and they see a freak, and he allows it because it provokes the reaction that he’s looking for. He proves people are prejudiced against his presence.

Professor X can’t do that. He can't risk KIDS AND TEENS getting hurt or attacked because of the way they look. He can’t risk being labeled a freak and an outsider and he can't risk his teachers and staff doing the same because then everything he ever worked for would come crashing down.

Let’s equate this to something real. Imagine that X-Men all an allegory for queer people (it is) and imagine Professor X ran a school for queer kids (he does) and his whole job was to convince super uptight conservative and religious parents to send their kids to his school. You bet your ass he’s gonna show up in his most Christian-clean-pressed suit, with a cross necklace and a rosary in his hands, clutching a bible, and wearing a ten-gallon hat if need be. He’s only gonna bring the masculine gay teachers, or the feminine lesbian ones, and he probably won’t bring trans teachers or students unless they 100% pass and look like the Mormon Tabernacle Choir because anything "weird" will make the parents go “hmm I don't like this guy’s looks”.

Does that mean he agrees with the parents' views? No. But he recognizes and understands them, and uses them to his advantage. He SPECIFICALLY plays off people’s prejudices.

And then? When he gets the queer kid safe? When they’re out of their parents' grasp? He hands them a rainbow scarf and a bottle of hair dye and tells them to go wild. He helps the trans kids get hormones, and binders, and makeup if they need or want them. He introduces them to other queer teens and adults and lets them live the life they want to live: an authentic life, and a safe one.

But in public? Wigs go on, disguises are in place, and pride pins and rainbow thongs are hidden. Not because he’s worried about his own image or that he thinks everyone SHOULD look and act a certain way, but because he KNOWS that society is still grossly judgmental and if a kid in a mohawk and sparkly eyeshadow goes waltzing around the city they’re going to get bottles thrown at their head.

Dropping the metaphor; if they need to go out in full mutant form, they get disguises. Uniforms. Armor. They get trained on how to protect themselves and CONTROL THEIR HORRIFICALLY DEADLY POWERS THAT THEY OTHERWISE COULD HAVE KILLED THEMSELVES OR OTHERS WITH so they can be safe and be authentically them and OUT if they want to.

I side with Magneto on a lot, but shitting on Professor X? NO. BAD. And entirely missing the point. Magneto has shown time and time again that he’s willing to let others die for his cause. Kids and teens and humans and mutants alike. Professor X is not willing to let a child die for him while still understanding that mutants want to, and will, fight for their rights. He walks a tightrope between “we need to fight for our cause” and “we need to protect each other”. Magneto has chosen to err on the side of fighting. Professor X has chosen to err on the side of protection. Magneto still protects and Xavier still fights, but that is secondary to their main cause.

Back to the metaphor; if you’re a trans person you worry about passing. If you don't pass, you could get attacked, assaulted, raped, or murdered. There are certain areas of the world where this isn't true. Times and places where you can be as out as you like. Pride is a good example of this. Drag queens will be out in full makeup and costume, but no queen, or king, or trans person, or queer anyone is going to advise you to walk down the street in Alabama at midnight in the same outfit.

Professor X and Magneto are both violently aware of the social prejudices against mutants. Professor X was and is able to hide his existence as a mutant due to his privilege as an upper-class white boy whose power didn’t manifest in a visible way. He has used this privilege to help people. Magneto, growing up during the Holocaust, was targeted for being Jewish and targeted for being a mutant. Due to this, he has chosen to make himself as visible as possible. He was tattooed in the concentration camps with a string of numbers that will forever mark him as “other”, and he decided to fully embrace that and challenge society to do the same. To him, the loss of lives is merely the price paid to push for change.

(via source)

Professor X’s focus, by contrast, is on the now. He prefers protection, and campaigns for change in subtler ways. He uses his privilege gained by hiding his status as a mutant to sway people’s opinions in other ways.

There is NO side that is without its flaws, but saying that “Professor X does nothing for the mutant cause” completely ignores the fact that he is doing everything he can to protect vulnerable groups like mutant children. His school flat-out RESCUES them from homes they might have, or HAD been abused in otherwise. If 5 years ago someone had offered me a device to magically make me look like a cis boy? I would’ve taken it and pledged my life to whoever had given it to me.

Hiding who you are is a terrible thing. Dying is worse. Given the choice between the two, most people pick the former. For those at peace with the risk of the latter, there is always the choice of Magneto’s side, and Professor X has never and will never forcibly prevent anyone from making that choice for themselves.