Picture if the guy was using a drug he was securing illegally, instead, and Mordo just . . . took away his drugs.
Or the guy was reliant on a manservant he'd enslaved, and Mordo freed the slave.
If you only consider the benefit to the guy in question, yeah, it seems cruel. They've made a point of establishing that Mordo doesn't see things that way, though. He's not causing the disability, he's merely taking back the coping mechanism that the guy has no right to, which Mordo sees as an abuse of that tool.
I'm not saying Mordo's right, just that it's not a clear-cut "kick puppies because EVIL" motivation. And still way more direct and honest than whatever's happening here; I cannot fathom Mordo being involved in the Hex and what it's doing to Wanda. If anything, he'd be more likely to be a third party who came storming into the mix to screw up EVERYONE's plans; Wanda, whoever's behind the Hex, the whole mess.
I get the impression that Mordo vs Wanda would be like trying to lasso an elephant, but that's a different story.