Though, if Soong really wanted his android as human as possible, it also would make sense to have no such remote turnoff.
I couldn't reliably say Soong DID want his androids to be as human as possible. If so, he wouldn't have made them extra fast/strong/durable, with greater cognition, heightened senses, & for a length of time not even passably human looking at all, like say Mudd's are.
What he DID seem invested in was creating the most advanced AI humans had ever achieved, & placing it in a vehicle that would give IT a comparably humanoid experience, albeit with the most advanced characteristics of any humanoid. He wanted to birth an AI, that would be able to live as a humanoid, & be somewhat confined to that, in order to shape its perspective of life from our own experience, while having it possess the practicality of interaction with the universe that humanoids possess, as opposed to some other kind of AI, like the HAL9000, or Skynet or something.
In all reality, there's really nothing to prevent a Soong Android from becoming more than an android AI, if it wanted to. I'm pretty sure the long game for Lore taking over Hugh's rogue Borg, was to eventually be able to seize control over the whole collective, supplant the queen, & essentially have an entire population as the appendages to his AI.
I like to think this is why Soong wanted his AI to be humanoid, to give it a respect for humanoid life that it might otherwise lack. I mean theoretically, if you knew an age of eternally developing AI were coming, and you had some concerns that it might in fact be the undoing of humanoid existence, one way you could go about trying to preventively curb that potential is by being the first to achieve it at peak levels, & then put it in a humanoid form. Literally have it walk a mile in your shoes.
Someone really needed to sit Data down & explain all this too him. The intent behind his creation wasn't for him to spend it trying to achieve a more human existence. The intent was for him to realize his own potential as what he is, & in some way try to reconcile it WITH a human perspective.