Abusive parent, spouse (and many other relations, don't forget employer) with control over one's computing is a big threat, and an additional weakness of self-hosting. But hardly a strength for anything else. This malware is for installation on an individual device, right? It doesn't matter in this instance whether network applications one is primarily using are P2P, self-hosted, or centralized. There's malware installed on your device, by someone with some trusted and/or coercive relationship with you. The relationship and whatever social systems enabling the relationship are the main problems, and which can't be solved by computing. Computing might be able to do something to make it harder to install and maintain malware, but again the architecture of network applications seem a wash for that. It's very easy to accept locked down devices as a mitigation; coming up with better is one of the most significant challenges for software freedom. Heck, maybe the most. As I've commented various times over the last years, though usually in context of people thinking locked devices a good way to mitigate outright device theft.