Rough Sex Defense
It is generally difficult to judge the merits of a particular type of defense through the lens of a small number of cases. This principle holds true in the "rough sex" defense, as reported in Time magazine in 1988.
Before turning to the defense itself, some exegesis is required with the article in question. The author, through (perhaps unintentional) use of language, is clearly unconvinced of the merits of the defense. Further, the world is a very different place now than twenty years ago. As the ease of communication and finding others with our own particular kinks, the relative embarrassment of asphyxiation play  is greatly lessened. In fact, in recent years the entire BDSM community  has emphasized safety as a key, defining element of the subculture. You can find safety, guidelines, and more for any particular type of sexual play fairly easily. It is arguable that the relative openness and availability of community for these types of fetishes effectively eliminates the merit of these types of defenses. Indeed, a cursory search of the literature indicates that while autoerotic asphyxiation is still occurring, incidents such as described in "The Rough Sex Defense" are extremely rare in the modern day. A cursory search of the internet for information (and warnings) about asphyxiation (or breath control) play are pretty easy to find.
With these elements in mind, it is difficult to accept Porto's defense, even in 1986. It is difficult to believe that admitting to brutally killing one's lover is more acceptable than kinky sex gone wrong, especially when the confession is repeated. If there were corroborating evidence (e.g. diary entries, notes, or other acquaintances who stated that she had wanted to date other people), it would definitely make the prosecution's case more solid.
This does not mean that accidents do not happen, despite the protestations of relatives who are unaware of their "innocent" child's sexual kinks. It is illogical and unrealistic to presume any person's kink or lack thereof - regardless of outward demeanor, age, or social class. What points to greater guilt in both the Porto and Bulloch cases are the actions of the men afterward: repeatedly confessing to murder, and trying to hide the evidence by torching the garage.
Still, given merely the evidence of death and Porto's testimony, it would be difficult to prove murder beyond a reasonable doubt. The eventual verdict of criminally negligent homicide seems to be the highest available with the greatest chance of conviction. As we have no access to any other evidence, it is impossible to determine premeditation or malice - especially since Porto's testimony contradicts earlier statements. It is, however, demonstratable and admitted that he did cause Holland's death through a lack of safety, thus providing grounds for conviction on criminally negligent homicide.
I would recommend the maximum four year sentence for Porto under the manslaughter conviction. Even if his story is entirely true - something of which I remain unconvinced - his passions overwhelmed any empathy or concern for others, thus rendering him temporarily subhuman. If it were possible to impose therapy during his incarceration, I would seek this as well.
As noted above, the "Rough Sex" defense does not appear to be very common twenty years later. I strongly feel this is due to the relative openness of the BDSM community, and their ongoing emphasis on safety. This undercuts the primary mechanism of defense. Our society's acceptance of deviant sexual practices - while still far from ideal - has surely progressed to the point where any type of sex is less shameful than murder.
 "Play" is meant in the jargon sense of sexual roles or acts that are purposefully enacted for the participant's pleasure, that are not typically part of mainstream sex norms or the everyday lifestyle of the participants.
 Asphyxiation is not equivalent to BDSM, nor do I intend to imply such. In fact, it's rather discouraged in that community because it's simply not safe. Being not safe, however, never stopped people.