Blessed are ye that weep now: for you shall laugh. - Luke 6:21
2. Blessed are they that mourn: for they shall be comforted. - Matthew 5:5
Note that Christ does not say "Blessed are they who laugh and take comfort in this present life," but blessed are you who mourn and weep in this world, and who reserve true comfort and consolation for the world to come.
King David in Psalm 125
1. When the Lord brought back the captivity of Sion, we became like men comforted. 2. Then was our mouth filled with gladness; and our tongue with joy. Then shall they say among the Gentiles: The Lord hath done great things for them. 3. The Lord hath done great things for us: we are become joyful. 4. Turn again our captivity, O Lord, as a stream in the south. 5. They that sow in tears shall reap in joy. 6. Going they went and wept, casting their seeds. 7. But coming they shall come with joyfulness, carrying their sheaves.
St. Paul the Apostle writes:
1. Therefore watch, keeping in memory that for three years I ceased not with tears to admonish every one of you, night and day. - Acts 20:31
2. For out of much affliction and anguish of heart, I wrote to you with many tears: not that you should be made sorrowful: but that you might know the charity I have more abundantly towards you. - 2 Corinthians 2:4
3. For many walk, of whom I have told you often, and now tell you weeping, that they are enemies of the cross of Christ. - Philippians 3:18
St. Isaac the Syrian
"All just men have left this world in tears. If the saints wept and always had their mouth full of tears ... who would not weep? ... If those who were victorious wept here below, how is it that one who is full of ulcers would cease weeping? A father, certainly, who has before him the body of a beloved child, does not need to be taught which thoughts will arouse tears in him. Your soul lies before you, dead through sin, and it is worth more to you than the whole world. If we go into solitude, we will thus be able to render tears perpetual. Let us then ask insistently that Our Lord give them to us. If we receive this gift, more excellent than any other, we will attain to purity through tears. And if we do reach it, that purity will not be taken away from us again until our departure from this world." ( Paul Bedjan, Isaac Ninivita, De Perfectione Religiosa, Paris-Leipzig, 1909, p. 252 )
The above quotes were gathered by another person at monachos.net message board but it conveys my ideas nicely. If Christ Himself (and His Apostles and Saints) did not advocate frivolity and easy laughter then it is doubtful that He Himself would go about guffawing like a fool.
The argument that "Jesus was fully human and so MUST HAVE laughed" is a laughable argument. Christ became like us in all things excepting sin, and most laughter, if we pay close attention to ourselves, is precisely the fruit of sins such as frivolity, worldliness, calousness and usually is a distraction and not spiritually healthy. Also, it must be remembered that Christ is also FULLY GOD and it is most probably blasphemeous to ascribe to God a sense of humour or "light-heartedness".