I'd hardly call F-Droid dangerous, these apps are generally safer than many apps on Google's Play Store. Sure, if you get some apk files from some shady website for the purpose of piracy, you are likely to get malware, but stop acting like installing apps outside of the default appstore is some dangerous and irresponsible thing. Your phone is a computer that lives in your pocket, treat it like you would treat a PC and you'll be fine.