If I don't use Passlock and my phone is stolen, I presume the first thing the thief will do is remove the Find My iPhone app from my phone - making Find My iPhone useless without Passlock??
You can't remove Find My iPhone because it's built-in. The Find My iPhone app is for finding someone elses iPhone which can be removed. BTW, Find My iPhone is for misplaced situation not a thief prevention. There is no way to prevent it.
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