Go see for yourself.
To reject heaven and accept atheism - is not merely about science, facts, beliefs, etc - it is about accepting the reality of all those who have died - being really dead. It is accepting the same reality about everyone you love NOW one day being - really dead. It is accepting the same reality about YOU one day.
The older you are, the more dear loved ones have passed away, the harder it will be to reject the notions of religion. To reject religion requires the re-mourning of everyone who you love who has died.
The complete post is quite long and just as good as this quote.