... what compels an athiest to tell the truth and not lie? It may harm his career if he gets caught or he might "feel" that he shouldn't, but as such s/he does not have to subject him or herself to any higher authority except for what s/he decides if this is in their best interest. So an athiest is not "restricted" to telling the truth, they may "choose" to, but they are not compelled by anything other than what the "choose" to be compelled by (e.g. standing in scientific community).
That's a really repugnant argument you have there. As an atheist I can assure you that I do not lie merely for the reason you have given. Simple
respect for someone else is a reason off the top of my head and in everyday life.
More specifically addressing your point, scientist have dedicated their careers to essentially
not lying (i.e. finding facts and giving truthful explanations for the facts). Career dedication; don't you think that counts for something? Look at Coyote's testimony (msg #72), he vividly recalls, almost painfully remembers, errors (unintended untruths). That's an example of career dedication and intellectual honesty. Look it up Arphy.