It is neither forced nor irrelevant.
@Frank Apisa's argument is this:
P1. If there is neither evidence for the existence of X, nor evidence for the nonexistence of X, then the existence of X is as likely as the nonexistence of X
P2. There is neither evidence for the existence of gods, nor evidence for the nonexistence of gods
∴ The existence of gods is as likely as the nonexistence of gods
P1 is obviously a ridiculous premise, or as
@Frank Apisa would say an "abomination."
There is nothing
forced about using substitution to point that out. Substitution is common as dirt in first-order logic. If you think my arguments violate any of the formal substitution rules, feel free to point out the specific rule and where you think it is being violated.
To illustrate how ridiculous the premise is, one has only to apply it to any random, ridiculous value of X:
P1. If there is neither evidence for the existence of X, nor evidence for the nonexistence of X, then the existence of X is as likely as the nonexistence of X
P2. There is neither evidence for the existence of a purple-and-green-striped-27-headed-cyborg-goat-with-rubber-duckies-for-hands, nor evidence for the nonexistence of a purple-and-green-striped-27-headed-cyborg-goat-with-rubber-duckies-for-hands
∴ The existence of a purple-and-green-striped-27-headed-cyborg-goat-with-rubber-duckies-for-hands is as likely as the nonexistence of a purple-and-green-striped-27-headed-cyborg-goat-with-rubber-duckies-for-hands
Or, one could also use it to refute
@Frank Apisa's own assertions:
P1. If there is neither evidence for the existence of X, nor evidence for the nonexistence of X, then the existence of X is as likely as the nonexistence of X
P2. There is neither evidence for the existence of proof that gods are impossible, nor evidence for the nonexistence of proof that gods are impossible
∴ The existence of proof that gods are impossible is as likely as the nonexistence of proof that gods are impossible
Since his entire argument is built upon that ridiculous premise, pointing out that it is a ridiculous premise is anything but irrelevant.