That he was derided because of his Excessive Clemency
Meantime, since there was no fear of capital punishment to deter from the commission of crime, for the emperor himself was uniformly inclined to clemency, and none of the provincial governors visited offenses with their proper penalties, this state of things drew with it no small degree of blame on the general administration of the empire; whether justly or not, let every one form his own judgment: for myself, I only ask permission to record the fact.
Source: Life of Constantine (New Advent)