The fact that the FBI has found a way to access the information on Farook's iPhone without Apple's help implies that they or some third party have found a vulnerability which allows them to bypass Apple's security. In the wrong hands, this vulnerability exposes millions of iPhone users to cybercrime.
The FBI should be required to submit this vulnerability to the Vulnerability Equities Process so that Apple can fix the vulnerability and protect their user's data.
The FBI should not continue to exploit the vulnerability in order to access other iPhones and leave the data of millions of iPhone users vulnerable to cybercrime.