Strictly speaking, counterfactuals must be true. If false then X is the same logical statement as If not X then True- which is true regardless of X.
You're treating counterfactuals as material conditionals. But there are many good reasons to think that counterfactuals are not simply material conditionals. One of the first observations that motivates work on the semantics of counterfactuals is exactly that some counterfactual sentences appear to be false -- despite having known-false antecedents.
In other words, people are bad at evaluating statements with known-false antecedents.
Today's post, Can Counterfactuals Be True? was originally published on 24 July 2008. A summary (taken from the LW wiki):
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