P1: If god exists, then there is ultimate meaning, etc.
P2: God exists
C: There is ultimate meaning
Gilson commits the logical fallacy of inferring the converse: It does not follow that the atheist, who denies P2 above, must conclude there is no ultimate meaning. Under the second form:
P1: If no god exists, then there is no ultimate meaning, etc.
P2: There is ultimate meaning
C: God exists
In this case, the atheist denies the conclusion, which means she must deny one or both of the premises. But we cannot infer from a denial of the conclusion which premise she denies.
Now, it happens to be the case that many atheists (myself included) also happen to believe there is no "ultimate" meaning. But this is beside the point. The denial of ultimate meaning is not entailed by atheism; at best, they are both entailed by more fundamental premises or hypotheses. But, logically speaking, there is no direct logical or analytic connection between atheism and any question of "ultimate" meaning.
Now, this philosophical mistake is so common among blinkered slave-morality Christians that it doesn't really qualify as "fucktardery". What does qualify is this statement:
Atheism entails that humans and animals and plants and bacteria and rats and pigs and dogs and boys (google the last four) are ontologically the same thing.This statement is so moronic and ridiculous that no sane person can take Gilson seriously or grant him minimal intellectual competence and good faith; we can only point and laugh.
[h/t to faithlessgod]