Similar things could deny the Borg technology as well as warm bodies: hair-trigger self-destruct mechanisms would leave them high and dry in their attempts at assimilating Starfleet spacecraft.
Considering the massive scope of the Borg community as revealed in VOY, though, it would probably be hopeless to try and affect Borg strength by merely denying them the use of a pitiful ten billion bodies per planet. On the other hand, among ten billion might very well always be one or two individuals capable of causing havoc similar to that created by Hugh or Icheb at their (re-)assimilation, just out of natural reasons. So better let those billions be assimilated than have them preemptively killed, statistically speaking.
Of course, Picard, our very own expert on the Borg, doesn't think statistically - in ST:FC at least, he quite specifically kills those at risk of getting assimilated. Since he's capable of ruthless calculation on many other occasions, he probably very well knows what he's doing there. This skipping of the chance that the victim might hurt the Collective might establish that Picard's Locutus side knows the chance is way too small to count.