Sea Breeze, Nicolaou did not say (at least in the post you quoted) that people can be happy without a purpose in life. Furthermore, he did not say (at least in the post you quoted from) that his purpose is to tell people that "they can be happy without a purpose in life". Instead he said the following pertaining to his purpose. "I have plenty of hope and purpose in my life, mostly centred around the people I love. Life is good without god." Sea Breeze please stop misconstruing what atheists say regarding atheism and naturalism!
I and many other atheists have a purpose (a multi-faceted one, not just of promoting atheism and naturalism) in life, it is a purpose I have chosen myself. My life is better without belief in YHWH God (and slavery to God and to religion), Armageddon, hell fire eternal torment, the devil and demons, and many other doctrines of supernaturalism. Many people don't need some alleged deity to assign a purpose to them. People can choose their own purpose! That is part of the great uplifting message of atheist naturalism! I prefer the purpose I chose for myself to the one the WT says is my purpose (namely to worship Jehovah God and to be a farmer in the new world) and to the purpose mentioned in the book of Revelation (of being a priest in the temple of God in heaven and of being a king).
It is not atheist's ideas on topic which are irrational. It is some of your ideas about atheist's ideas of this topic which is irrational. The supernatural ideas of Christianity are what is absurd - not atheism and scientific naturalism!
There is something though that I greatly appreciate about the WT's JW religion. It is the idea that all false religion will come to a complete end. I relish that idea. I too want all false religion to end (though I don't expect it will ever happen as long as our species continues to exist, but it can greater become far less prevalent). But I want it to end without people being forced to be nonreligious. I want religious people to voluntarily cease being religion (such as a result of persuasion and of them drawing their own conclusions in the matter). I want all beliefs in the existence of the supernatural to cease! The world and human society would be so much better if such was the case (provided it was not due to coercion)!