I agree with my friend that he should not have told this individual to go to hell. But the incident has had me pondering the expression a great deal. I understand the impulse, but it was the wrong thing to say, in part because it was pointless. It was the pointlessness that had me pondering. I can think of two cases when there is no point to using the expression.
1- One group of people to whom it is pointless to tell to go to hell is those who are already living in hell. These can include the molested, the abused, the persecuted, those suffering the consequences of others' poor choices. (For the moment I will set aside those suffering the consequences of their own poor choices). These individuals might be forgiven for wondering how much worse hell might be than what they are suffering at present. God might know but I do not.
2- There is another group of people on whom the phrase is wasted. These people make everywhere they go into hell, either for themselves or for others. They are like the devil; "he seeketh that all men might be miserable like unto himself" (2 Nephi 2:27). One of these people could be sent to heaven and he (or she) would not be satisfied until he had turned it into hell and proudly point back to the good intentions lining his path. There are those, of course, who make a hell for others and then refuse to live in the hell that they have created or sometimes even visit; they may yet have their chance.
Of course, for us mortals, telling people to go to hell reflects only a wish on our part. We have not the power to compel or order people to go to hell for real even if we have the power to torture and torment others to the point where they think they are there.
There is one who can tell someone to go to hell, and that is God. Whomever God tells to go to hell will no longer have any choice in the matter.
Some people think that it would not be just for God to send people to hell. They "do try to suppose that it is injustice that the sinner should be consigned to a state of misery" (Alma 42:1). The sinner's victims might disagree with that thought. Alma explains that God provides sinners a way to repent and time and opportunities to do so and thus his decisions are just (Alma 42). If they choose not to repent, they have no one to blame but themselves.
Others think that it would not be merciful for God to send people to hell. Moroni deals with this argument:
Do ye suppose that ye shall dwell with him under a consciousness of your guilt? Do ye suppose that ye could be happy to dwell with that holy Being, when your souls are racked with a consciousness of guilt that ye have ever abused his laws?God will send some people to hell precisely because he is merciful both to the perpetrators and the victims.
Behold, I say unto you that ye would be more miserable to dwell with a holy and just God, under a consciousness of your filthiness before him, than ye would to dwell with the damned souls in hell.
For behold, when ye shall be brought to see your nakedness before God, and also the glory of God, and the holiness of Jesus Christ, it will kindle a flame of unquenchable fire upon you. (Mormon 9:3–5)