Presidential pardons are assured by the Constitution of the Unied States of America. If Congress and the rest of the nation doesn't like presidential pardons, they can amend the document. Whether presidents are perceived to abuse this power is irrelevant--the chief executive has this power until it is taken away by legal means.
The president of the United States should not have any right to decide whether or not a criminal should be pardoned. This is why we have a court of law in place in our country. The courts will decide whether or not a person is guilty based on evidence and factual accounts of what happened.