I was listening to a Christian, not specifically Catholic, radio station and the speaker stated that for a believer to worry was to sin because it shows a lack of trust in the wisdom of God. He saw no problem for non-believers to worry because they have a lot to worry about in this life and the next. Your thoughts?
Sin requires an immoral action, sufficient knowledge, and sufficient consent. To the extent that it keeps us legitimately concerned about the welfare of ourselves or others, it is not an immoral action to worry. Even in cases of needless worry, most worriers do not purposely worry despite knowledge that they should not. Indeed, in some cases, excessive, compulsive worry may be a symptom of a legitimate illness, and therefore not a sin.
You reported that the speaker you heard stated that worry is actually a moral good for some people. If that is the case, worry cannot be a moral good for some people and a moral evil for others. Worry, in and of itself, is morally neutral; if a person cannot control a compulsion to worry, he should seek medical and/or pastoral advice.
Understanding Scrupulosity** by Fr. Thomas M. Santa, C.Ss.R.