If the use case is as described (connecting to WiFi APs owned and controlled by the network in deadspots / hotspots - e.g. stadiums and large buildings - and not end-user APs in homes), it's not clear to me that this poses any significant threat above and beyond connecting to the same operator's cell towers. If you don't trust them to run a WiFi network, probably shouldn't trust their cell network either.

Having phones automatically and uncontrollably route via random 3rd party APs is a bad decision, but I didn't read GP as advocating for this.