When Paul wrote that the Fruit of the Spirit was embodied in, among the other eight, "goodness" he made the tremendous, yet very unpopular, statement that the idea of goodness deficient of godliness is false. But, how can this be when there are so many "good" people which live outside of Christ?
If we are to imitate that which is good (3 John 11) and God is the only one that can ultimately be deemed as good (Matthew 19:16-17) then the modern idea of goodness is to fall by the wayside and be surpassed by godliness as the definition of what is good. Throughout the Scriptures, the Christian is instructed to carry out works in "meekness of wisdom" (James 3:18-18) which can only be done through "good conduct" which, as defined by James, is a life separated from envy, boasting, lying, confusion, partiality and hypocrisy but having within it peace, gentleness, a willingness to yield, and full of mercy and good fruits. That is true goodness and since all of these things which are part of the works done by meekness of wisdom are directly commanded and defined by God throughout His word, the only source of true goodness would have to be the Bible.
Is it possible to be a good person outside of Christianity? A study of the divine Book would say no. Since that is the case, and the person obeying the Gospel is said to be doing so based upon a good/godly conscience (1 Peter 3:21) then it is safe to say that the only good people are New Testament Christians. I know that is a very controversial statement, but that seems to be the only answer to the question of "Can a person be good without God?" And, if the Christian is going to maintain that good conscience which led him to become a child of God (1 Peter 3:16, 21) and answer the questions posed by the unbelieving (1 Peter 3:15), then he will have to answer in the negative in spite of any reviling and defaming which might come his way because of the answer because it is better to suffer for good than evil(1 Peter 3:17).