I think it's just human nature to not want others to believe falsehoods. If someone else's belief in falsehoods may also affect one's quality of life, then motivation to convert them takes on a degree of self-interest, but not unreasonably so.
In the context of religious discourse, if religious folk are correct, then there's an added element of cognitive dissonance for the unbeliever, as beings created in the image of God undergo spiritual warfare (whether they recognize it as such, or not), duelling internally, as their conscience battles with their limited, but oft-overestimated, reasoning ability; overestimated in comparison to that of their spiritual foes. Perhaps this gnawing away of the conscience is alleviated as others - whose witness may otherwise exacerbate the unbeliever's malady - cease to hold them to account. A situation not too dissimilar from that of the first reading at Mass only yesterday:
{Wisdom 2:1, 12-22}If religious folk are incorrect, then I can see why atheists would want to convince them otherwise - referring back to my initial motivation for correcting error - but I find the ardent commitment to such a cause somewhat disproportionate. Perhaps contributing to this is the fact that the subject area is in itself fascinating, and tends to incorporate other fields in its wake. It does, however, seem odd that an unfounded belief would have such wide-ranging impact, interest and durability; but perhaps this is the inevitable situation for any sentient being with the capacity to conceive of eternity.
