Totally agreed with longchen and bohiruchi.
When confronted with such a kind of situation, I always see it as
similar to explaining to a person who is visually- impaired since
birth the concepts of colors. Its extremely tough for both
sides.
We know of different colors becos we can see, but to a
visually-impaired person he/she must be very special to be able to
understand the diffference of red , yellow or blue without tangible
terms. They can feel the tangibles, but must be highly enlighten
enough to feel "colors".
So, yeah, for normal sentient beings like us, can only have
constructive arguements when both sides have equal "weapons": Eyes.

I've posted the quote below in " Daily Buddhism Verses", but would
like to post it here again as a closing.
Do your best each of you; go wherever circumtances lead
you.
With those who are sympathetic
You have discussion about Buddhism.
As to those whose point of view differs from ours,
Treat them politely and try to make them happy.
Disputes are alien to our school,
They are incompatible with its spirit.
~ Hui neng