How does that have anything to do with requiring users to have an account to download software signed by Apple from Apple's servers? That doesn't make a lick of sense to me.

This problem was solved years ago with code signing.

Running unsigned code requires several hoops, even running signed code which isn't Apple Approved requires telling the OS that you know what you're doing, twice.

Running signed code which has been altered, such as a hacked XCode, isn't possible, as far as I know.

If this was the reason developer accounts were required, it no longer is. From Apple's perspective, there's only upside in requiring them, which is the most likely explanation for why they do.

Not developer tools that are downloaded from apple.com.