Lol - sap reminds too much of the vital fluid of plants - or of the verb used for undermining - among other definitions, but not of stupid.
How about Homo stultus? Or do you prefer Homo caecus - and that applies for both genders (Love is, usually blind, and might even be considered as a state of sickness) ...
But T(h)ink's theory about a previously existing condition (a disease, a weak point or a flaw?) could also apply.