Another way to think about this question, rather than the old and tired argument of occult-players vs non-occult-players, is to look at it as a way of giving players control over random generation of sims in general. Including the human sims.
A lot of players (both occult and non-occult) don't really like randomly generated sims at all. Their trait combos tend to be bizarre, and their outfits are horrendous. They flood the venues when you're out and about and make it hard to actually meet the pre-made sims or the player made sims, because they take up slots in the total limit for how many sims can be on a lot.
Allowing players to choose whether the game randomly generates sims or not is something a lot of players have been asking for.
Controls to allow or disallow the random generation of individual types of sims (human, alien, vampire, etc.) would just be a fine tuning of that idea. With these options, you certainly could create a "humans only" save by blocking all the other types and deleting the pre-made ones. But you could also use population control settings to create an "aliens only" save or a "vampires and spellcasters only" save, for example, if you wanted to. Personally, I'd really like this.
It would also be useful if you want the occult sims you created, or the pre-made ones, to be the only ones you see. No more goofy random vampires prowling the streets at night. Just the cool looking ones you spent so much time creating.
Population toggles for random sims wouldn't solve everything (for example alien abductions would need its own settings) but having them would give players a huge range of options for customizing the look and feel of their games, regardless of whether they play with occults or not. I feel like it's something most players would actually be on board with.
