Why Apple refuses to obey to the FBI and unlock the iphone?

The Apple company with headquarters in Cupertino noted in its response to the United States Department of Justice, that the government has resorted to force the collaboration.
The FBI has asked the company to design a software that will allow you to enter the security system for an iPhone that was used by one of those involved in the shooting of December in the city of California in the United States, I leave the balance of 14 people killed and 22 injured.
Apple considers that the court order that requires you to collaborate with the Government violates the constitutional right of the company to the freedom of expression, but while the Department of Justice of the United States I take it as false the discussion of Apple and made that the government and the community need to know that there is after the iPhone of the terrorist that provoked the murder of these people, the government needs the help of Apple to discover it and this refuses to unlock the appliance that goes against the privacy of users.
The terrorist Syed Rizwan Farook, who was shot dead by police in San Bernardino california.
The question that everyone will do is Why Apple refuses to obey to the FBI and unlock the iPhone of the attackers San Bernardino?
The aim of the Government of the United States is to know if there were accomplices of the couple and find out possible links with the self-styled Islamic state and other terrorist groups, but for all this the company has refused to make what now commanded the justice.
In one of the analysis made by the BBC to understand the importance between the complexity that Apple and the FBI have about the phone section were the following:
The FBI wants that alters the so called System Information file or SIF, the software used by devices, and create a new one, this would enable them to carry out various functions that cannot be done in the current phones, but this is not easy because Apple from 2004 to encrypted all systems of the iPhone so that neither the same can decrypt what the user is doing.
But the FBI argues that only wants to access the iPhone of the terrorist of San Bernardino califonia farook through a system that only Apple know and that will destroy subsequent to the investigation.
Now the response of the Apple because it resists to collaborate in research that is taking the government, in a report to its users, the chairman of Apple, says that they do not want to create a door, alterativo system to access a iPhone apart from entering the password.
The rear placed are crucial in security the computer or hackers can Piras and make real fortunes if the discovered and the buyers who try to decrypt and spy on any target for damage to users including the government.
Most of the experts say that it is possible to access the iPhone of Farook without damaging the data it contains, Apple has not denied that this is possible.
Who supports Apple?
We cannot allow the establishment of a precedent so dangerous, in these times our freedom is at stake, this said Jan koum creator of WhatsApp.
Forcing companies to allow hackers could threaten the privacy of the users, while the FBI is creating a world where citizens depend on Apple to protect their rights, this was said by the head of google, Sundar Pichai.