How do you not invest some curiosity in what they are "selling"? Doesn't "what if" ever haunt you?
Curioiusity is great. And your question I think merits further thought.....
I don't think it healthy for anyone to stay in one place. We must grow, and we must consider the possibilities.
However, it isn't healthy to sacrifice "what is" for "what if".
What we know is that many theists are willing to sacrifice now for the future. It is all positioned on this single thought: The end of your human life isn't the end of you.
Sin = death. (i.e. the end of you) Theists offer life heretofore unseen and unproveable if you agree to worship an invisble god. The only possible thing that could motivate a person to keep this up is to scare them.
"God doesn't approve of you or your actions." "You are sinful." "Believe, exercise faith, or die forever. Believe, and you will live after death."
Death is scary, and it is the biggest bugaboo religion throws at us.
The problem is, despite milleniums of time, not one claim has been proven. Meanwhile, history shows us "what is". That is to say, the effects not of sin, but of the teaching of sin....
There are benefits to those who teach it; power, money, control. Not all use this cynically, but most have.
A discussion of sin obscures the more important discussion regarding aspects of productive human behavior. When we can use the critical analysis and thinking faculties we all posses, we can filter out what is good productive behavior from that which is superstitious and designed to somehow appease the invisible deity, but which in actuality enslaves people to man made religions.
To deny sin isn't to deny that which is right or wrong. It is a different, non theistic perspective that puts humanity and love on a higher priority over sin and trying to appease "god".