I’d like to!
Releasing an app that supports an OS with known security vulnerabilities doesn’t mean you are encouraging usage of said OS. There are many reasons why people are still using said OS, and most are likely not doing so by choice. People buy a phone, and are stuck relying on the manufacturer to update it. Most people can’t just go out and buy a new phone because Motorola, LG, Samsung, or whatever manufacturer they have decided not to update it anymore. Even if Google backported the fix to Android 4.1, most of those devices would still never see the fix!
Actively preventing people from using an app that would work perfectly well on their phones/tablets seems like a bad way to make a statement. If you want to prevent people from using OS’s that have known security flaws, why does Discourse work on XP and earlier versions of Windows? Why support older browsers with vulnerabilities, and not just the newest ones? It just seems very specific that Android is being targetted here, and nothing else. I might be able to support this if the same stance was applied to everything, but targeting one OS is wrong.