Perhaps you might worry about hostile IOT doodads snooping on things that arent their business or making insecure public webpages with UPNP. If it is just devices you truly control and you never expose an unhardened device, then a walled garden can be fine.

Also, if WPA2 ever becomes extremely broken. There was a period of 3-5 yrs where WEP was taking forever to die at the same time that https was taking forever to become commonplace and you could easily join networks and steal facebook credentials out of the air. If you lived in an apartment building and had an account get hacked between maybe 2008-2011, you were probably affected by this.