oh no no no no......
i really must strenuously disagree with you here. so many times i have had bible bashers stop me in the street or knock on my front door. perhaps they are taken aback when i invite their conversation, as opposed to introduce their face to the door?
i am open minded enough to know that somethings we do not know. i indulge in probability in order to find that evolutionary answers to be more compelling than the theological... but that is not to say i presume that no sandle wearer would never make sense.
and of course the more empassioned their rebuttal of your calm and rational POV is, the more indicative it is of your undermining their beliefs. afterall, as many of us can appreciate, religious followers are usually created thru familial pressure enforcing habituation.
do not preach; just explain why you do not agree. we know that there is an inherent selfishness in us all and even the most devout will one day want pay back. circumstance might just conspire to test their faith before death and at that point, our 'evil' non-believing words might 'set them free'?
or maybe it will have the opposite effect. but either way they benefit, as will you! so try. spread the good word.
incidentally.... every time a religious nutter has cornered me for an 'enlightening chat' it is they who make the excuses to be on their way! how rude!