Because God is never cruel, there is a reason for all things. We must know the pain of loss; because if we never knew it, we would have no compassion for others, and we would become monsters of self-regard, creatures of unalloyed self-interest. The terrible pain of loss teaches humility to our prideful kind, has the power to soften uncaring hearts, to make a better person of a good one.
People do need a social license to go, "Ha ha ha," and have a good time. It's a strange thing. There's a lot of social ritual around comedy and laughter. It's a bonding experience for groups, but nobody can tell you much about how funny somebody is. Sometimes people just need to be in a group and be laughing together, just like they need to be in a group in watching some really terrifying film.