wtf. I have been using F-Droid for many years, and this has not been the case. as far as I know, this has never been the case, as Android has always had functions for third party app stores. in fact, even today, F-Droid recommends not using root for installs, since then you don't get the screen showing permissions.
> allow third party code
that's called running apps.
tl;dr nice FUD.