I guess we all know that the real reason why pon farr was mentioned in "The Cloud Minders" is because the people who were rewriting scripts to make them consistent in Seasons 1 and 2 had left the show by Season 3. In his second autobiography
, Leonard Nimoy reports that the initial script for "All Our Yesterdays" had Spock eating meat and falling in love with Zarabeth with no explanation whatsoever, and when he pointed out to Fred Freiberger that Spock wouldn't DO such things, this was news to Freiberger. So an awful lot of things happened that shouldn't have happened if the show's producers were being consistent ... or if they actually knew
anything about the show that they were supposed to be in charge of.
Miss Manners says that the proper response to someone farting in public is to simply pretend that it didn't happen. I know that the usual fan idea is that anything that happens on-screen is canon, but I think that certain elements of Season 3 should probably be ... delicately overlooked. Pon farr mention in "The Cloud Minders"? What pon farr mention in "The Cloud Minders?" I didn't see that, noooooo.
As for why Vulcan mating is violent and messy, it's because Roddenberry wanted it that way.
In his second autobiography, Leonard Nimoy quotes from a memo that Roddenberry sent around in May of 1966:
[Emotional repression on Vulcan] probably led to a need for hypnosis as a part of the sex act, and we may gather from time to time that love on Spock's planet has a somewhat more violent quality than Earth's aesthetics permit mankind to enjoy. (Unless NBC changes its policies somewhat, we will probably not do an episode dealing directly with this subject.)
(Italicized quote taken from "I Am Spock," by Leonard Nimoy, first hardcover edition, page 66.)
I suppose plak tow could be considered similar to that hypnosis that Roddenberry thought Vulcans would need to be able to get it on -- it's an altered state of consciousness that leads Vulcans to do things that they wouldn't ordinarily do.