I think I've written this before, but: this feature would go nowhere if it was disabled by default. If you want to know whether mainstream users will or will not like it, you can't stick it in some obscure alpha (they'll never test it), and you can't make it optional (only a few percent will ever come across the tick box at all).
So yeah, I don't like this feature either (for all the reasons RMS pointed out), but I don't see how otherwise they could have tested it. Maybe not a failure of judgement then, but rather choosing innovation over privacy?
(Note the 12.10 betas also had all these queries going over the network in plain text... so I kind of see the whole experiment as taking the "move fast and break things" mantra taken to the extreme)
Opt in doesn't necessarily mean hidden in settings. For this feature it probably should be a pop up that appears the first time each user enters a search request before it gets sent over the network.