Why is the father always blamed when a son turns out to be a scumbag, regardless of whether he was present during his upbringing?

When a son grows up with both parents and turns out to be a scumbag, people blame the father for failing to raise him properly. Yet when a single mother raises a son who turns out the same way, the absent father still gets blamed for not being there to teach him how to be a "proper man."
But surely, if the father wasn't there, wouldn't that have given the son the best possible chance of growing up without becoming toxic, since his father wasn't around to teach him any of his supposedly toxic traits in the first place?
Why is the father always blamed when a son turns out to be a scumbag, regardless of whether he was present during his upbringing?
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