It was possibly the late Ambassador Sarek who said it best: "My logic … is uncertain, where my son is concerned."
Most non-Vulcans do not quite understand what was said there. It was not a confession of weakness, or an aberration on Sarek's part from the Vulcan norm. It was a simple statement of fact, for which no other Vulcan would have required an explanation. "My logic … is uncertain, where my son is concerned."
The Vulcan phenomenon of pon farr, once almost unknown to non-Vulcans, is now (relatively) common knowledge; even a source of risqué humor for the other races. It is a time when biological imperatives overwhelm and supercede the trained rationality of the adult Vulcan. Ironically, this stripping away of a Vulcan's logic is, itself, highly logical; the survival of the species requires that certain biological imperatives have a much higher priority than any imposed system of rationality and emotionlessness. One of those biological imperatives upon which the species depends is sexual reproduction – and thus, pon farr.
Another biological imperative, upon which the survival of the species depends, and which carries a higher "hard-wired" priority than any learnéd philosophical system, is the protection of the children. One threatens the children of a Vulcan at one's own great personal risk; for whereas plak tow (the "blood fever" which accompanies pon farr) is primarily self-directed, and may be fatal for the Vulcan in whom it occurs, the violence which can result from a Vulcan defending his or her child is completely externally directed.