I feel I also need to re-quote the OP:
...why don't Christians have an irrefutable argument that no unbeliever could deny?
To be brutally frank, smug responses that insinuate that atheists are too blinkered, or whatever, don't really cut it for me. If there is a supreme omnimax deity that created the universe and everything in it, then it should go withour saying that that being could have easily and simply ensured that a genuinely
irrefutable argument was available.
And not just available, but so "in your face" and obvious that Christians would be comparing it to the argument that "night is dark" and declaring the latter far too complicated and obtuse. There is a PC in front of me, my shirt is blue, the time is 13:22, god exists. Anyone and everyone in the same room would be entirely unable to refute the first three points - would not even bother attempting to try - so why, with an omnimax god, is the fourth such a different proposition?
That's what I just don't get: why it is possible for us to be having these arguments over the "irrefutability" of GOD
in the first place. Think about it, believer guys. Why are you not able to say "well, the irrefutable argument for god is this.....", and have everyone just go "oh. Yes, of course. Obvious. No arguments there."? Not just today, but for the last few thousand years?