I can tell by the fact that they refuse to claim their salvation joyfully, but think it humble to say they won't know until they die. God wants us to be assured of it! How on earth does a person show Christ to the world when he has no real hope?
Consider that Catholics not only do have hope, but embrace virtue of hope possibly more so than I've experienced in my Protestant years. Am I saying Protestants don't have hope? Of course not -- but it isn't fair to suggest Catholics don't when they put such an emphasis on hope itself. It is the second of the three theological virtues that we cherish.
Our salvation is expressed with much joy.
I suspect you get distressed when you see someone who claims to be a Christian throwing in the towel so often -- I do too. You aren't alone in that feeling. Though to suggest Catholicism itself is wrong because of the misbehavior of some Catholics who have abandoned the faith is bad criteria. Wouldn't it be wrong to suggest Protestantism is wrong because of Westboro Baptist Church who claim to be a Protestant church?