Oleanders are very heavily used as landscape plants all over the world. As are many, many other plants that are poisonous. Small children and pets are more likely to chew on houseplants.
There are many cat poisonings by potted lilies. The leaves look like grass. Don't get potted Easter lilies if you have indoor cats.
Other common poisonous plants include: Rhododendrons, Azaleas, Ivy (All of the Hedera helix ivies, common ivy, English ivy, Algerian ivy too)
Daffodils
Datura, Brugmansia, Castor beans
Philodendrons, Dieffenbachias
If we stopped growing or selling all plants that are poisonous in some way, our gardens would be half empty!