It's not good in principle. There are many legitimate uses of writeable code pages, and as long as they're not the default they are unlikely to cause security problems. Don't forget that these apps all run in a sandbox already, so an app exploit won't get you system access anyway. All the excuses Apple/Microsoft give are just that: excuses. The real reason interpreters and self-modifying code are prohibited is to prevent competition with the first-party browsers and app frameworks.