Many readers guessed that Arno would end up evil. The name is a dead give-away for any Marvel history fans, given how the previous Arno Stark was the evil Iron Man of 2020. There's also the long tradition of villains being handicapped or otherwise deformed, because of course people who look or function differently are the Other and are cast under suspicion. There was some hope that Arno would end up being a nice guy, since he seemed pretty amiable and he even referenced the "Evil Cripple" trope when talking about his reticence over becoming a public figure like his adoptive brother.
These hopes were dashed in the latest issue, when it was revealed that Arno was working on a new serum of Extremis. Yes, Extremis, the super-deadly biotech serum that weaponizes human beings, and often makes them monsters. The kind that temporarily infected Tony's body, saving his life and boosting his performance as Iron Man (as well as giving him wacky super-powers like mind-controlling satellites and healing from injuries to the point of being able to reattach a severed heel) but also driving him mad with the traumatic flow of new information, to the point of entering fugue states where he talked to "ghosts". And the kind that Tony's tried to eradicate in this very volume, seeing its grotesque potential for misuse even by people with good intentions.
It's possible that we're meant to sympathize with Arno, because of Extremis also has potential for beneficial medical applications. But all that potential means nothing given the circumstances, such as...
1.) Arno isn't doing this to help other people. He's doing to help himself, so that his lungs can be fixed and he can live without external support. Never mind the fact that his external supports give him far more capability than most people, since he's at least as smart as Tony and builds his own powered suits. He wants to be cured, even if he has to use a super-deadly monster-serum to do it. Basically, he's using Curt Connors logic.
2.) Arno has no real identity outside of being a genius and being disabled. We don't really get much indication of Arno's thoughts and feelings beyond what the plot demands. Even though he spent most of his life in seclusion, he could still think, feel, and dream. Even without an exoskeleton that gives him mobility, he's got all those capabilities. But we don't get to see those capabilities, because all we get from Arno is what he does with Tony Stark, and now what he's doing to undermine Tony Stark. The hints of Arno's life outside technology and envy of working lungs, such as his interview with ultra-leftist reporter Abigail Burns, are only told and not shown.
3.) "Magical" sci-fi cures tend not to end well. This may be so common it's become cliche, but there's a reason writers don't often write stories where there are pills that can fix all ailments. Fiction is the place where people, creators and audience alike, work out their anxieties and achieve a meaningful catharsis. Sometimes it's the place where people hide from reality and go straight to escapism, but certainly Kieron Gillen is a savvy enough writer that he wouldn't just go with "Arno uses serum to fix his lungs, succeeds in doing so, then uses serum to fix world, and creates a Candyland Utopia where nobody feels bad".
Some have criticized this mentality as anti-progress and anti-science. Certainly that's a result of the bizarrely static nature of the Marvel Universe, which has to remain similar to our reality and can't allow the super-scientists to radically change our infrastructure. But the implications of the alternative are much more troubling. If this form of super-science solving everything is a reflection of a desires, that means we see a world of easy answers. Where every problem has a solution, and those solutions can be universally applied across all kinds of problems. Where we get to see the happy ending while skipping past all the hard work and tough decisions needed to get there. Where we trust that we can take a pill to make ourselves happy and healthy, and not have to worry about the side-effects. And worst of all, where we see being infirm and disabled as something that has to be completely eradicated, and can't comprehend the notion of people being okay with the way they are (or at least being okay enough with their disabled lives that they wouldn't risk their lives on a potential cure. I'm not downplaying the challenges that come with physical and mental disabilities; I'm saying that they AREN'T fates worse than death, the fate that gives you absolutely no other options. They're certainly not worse than "dying" by virtue of turning yourself into a monster and losing all sense of self).
Arno says he wants to use Extremis as a universal cure, one that can be applied to all medical problems. Arno is confident that he can work out all the bugs, even though no previous scientist has done so. Even if he does avoid that particular consequence of his hubris, Arno's still making himself the authority on what should be cured and what shouldn't. Perhaps Arno will decide that homosexuality is a disease that needs to be cured? Perhaps he'll decide that darker colors of skin should be swabbed away by Extremis? And perhaps when people such as Tony Stark, a man whose adult life has been defined by physical and mental weaknesses but hasn't let that stop him from doing the right thing and avoiding the easy way out, oppose Arno's mentality, he'll decide to use force because his will is more important than anyone else's?
I know that it's a slippery slope argument, but by all accounts Arno's slope currently is devoid of any and all friction. I sincerely hope that the next issues will prove me wrong.