I don't see what skeptics have to offer as "cold harsh reality" or "nothingness".
If I believed in religion, a lot of them anyway, I would have to believe that my father was burning in hell and suffering for all of eternity because he was not a believer in any religions or gods. That's comforting??!!
Instead, since I do NOT believe in any religions or gods myself, I can reflect on my father's years as a scientist and how he contributed a great deal to the body of human knowledge. He donated his body to science so that his disease (cancer) could be studied and perhaps defeated someday. There is no more suffering for him. His legacy will go on for long after I am gone, and THAT I find comforting.
And believing a bunch of errant nonsense is not really a freeing, comforting thing either. Most people limit their lives and experiences because they believe it's a bad day for their biorythms, it's against their religion, their horoscope told them not to, or their psychic advised against it. A friend of mine spent weeks alone in her house wearing a hepa mask, because she believed it would cure her of all the things she was allergic to, and the list was very long. And how did she know she was allergic to all these things? She held the substance in her hand, and if her hand moved down to the ground it meant she was allergic. !

(I was tempted to ask if she was allergic to bowling balls, but I restrained myself.)
The skeptic does not get concerned about biorythms and such, but can get out there and enjoy life every single day. Instead of looking at the wonderful complexity found in the eye, giving up and saying "god did it", they can study and learn and find out how truly marvelous life and the world can be. They can learn something new every single day of their lives, because they don't need to worry that education might challenge their belief. Now, that is freedom.
And simply because the skeptic is not constrained by a belief in eternal punishment, that does not mean they will be socially destructive. As many have pointed out here, it is very easy to tell if someone wishes to hear about skepticism, or if they do not. And the truth is, it is very hard to shift someone from their belief. In fact, they have to do it themselves.
So I think the imaginary person in the OP will continue to cling to their belief because they wish to. As far as whether I personally would say anything to such a person would depend on circumstances; but I believe that the knowledge would set that person free for a richer life, not diminish them somehow.