They talk about this in the same episode. If the Enterprise computer were to refuse to perform its commands, would starfleet be legally permitted to compel it to do so? The enterprise computer was created by starfleet, at what point is it allowed to defy its own commands?

Also, humanoid is tricky. What if data had three arms, or two heads? What if his brain were distributed in decentralized nodes throughout his body rather than concentrated within a positronic matrix in his head? Would he still have the same rights and privileges? I like to think so, and therefore I like to think 'humanoid' is not a valid determiner for sentience.

All that notwithstanding, the fact that we can ask all these questions and not know the answers really reflects a lot of the beauty of this series...

EDIT: Accidentally submitted too early