PGP 2.3.a had an interactive mode by default when importing keys (e.g. from a file).
GPG does not even have an option to enable "interactive import" of keys.
An "interactive import" is a mode where GPG will ask before importing a key or additional signatures whether to add or whether to ignore them.
As most users don't know whats in a public key file, it makes sense to have an interactive import mode IMHO.
It does not matter what you have in you keyring. It does not harm to have arbitrary keys there.
But it might make sense to have such an option in Kleopatra - will be much more user friendly than an interface like gpg's --search-keys.
Well, I think it's a matter of taste what keys a user wants to have in which keyring. Some users want only the keys they actually use.
I think policy or the algorithm should not take the decision away from the user. "Free software for unfree users" doesn't make much sense. Maybe I'm just so old that I still think the computer should do what the user wants it to do, and not the other way around (which seems to be a current trend).
Nobody stops you from removing any unwanted keys from the keyring. Nobody stops you from importing all keys to a temporary keyring (using a temporary GNUPGHOME), export only those keys you want in your proper keyring, import those in your proper keyring, and then ditch the temporary keyring (resp. GNUPGHOME). gpg doesn't stop you from doing any of this.
And, of course, you are free to propose a patch which adds this feature.