"Ýnsan, bu dünyanýn olumsuzluklarýný  unuttuðu sürece mutludur.

  Bu nedenle, prensip olarak, hayatta daima güzel ve faydalý iþler yapmak; herkese anlayýþ,     saygý ve sevgi ile yaklaþmak gerekir.Bu ayný zamanda, insan olabilmenin gereðidir.

  Ãnsanlara adil, vicdanlý, iyi ve güzel davranmak mutluluktur...."

 My try:

Man is happy as long as he forgets the negative things in this world.

Therefore one must always do nice and useful acts in life, and approach everyone with understanding, respect and love. At the same time it is the need of being able to be human.

Treating people fair, conscientious, kind and nice, that´s happiness...

INSAN : Human being

I think ´man´ is a perfectly acceptable translation in this context.   

(in the first sentence anyway-modified)

I expected someone to comment on the translation of: insan olabilmenin gereðidir.

(my translation: it is the need of being able to be human)

It´s a strange sentence, and It doesn´t really ´fit´ in the text this way.

Thank you very much