Why is the power of the president to pardon so controversial

It is controversial because the President can pardon anyone! Take Nixon and Goldwater for example. Nixon was convicted of spying on th opposite party. Nixon stepped down, but was still charged. When Goldwater became president, he pardoned Nixon of all of his charges which caused a huge uproar. That's fair, right?

It is very controversial when the president pardons someone that a jury has determined to be guilty. Why even go through the court process?