Rather than attempt to paraphrase further, I will let ABFH speak for herself:
Here's a brief scenario to illustrate the point: Let's say a mother takes her two young children, one of whom is autistic, with her when she does the grocery shopping. The autistic child starts crying because he is overwhelmed by the bright lights and the busy, crowded, noisy environment. The mom grabs a few groceries and hurries to the checkout. Then the non-autistic child starts whining and crying because the mom wouldn't buy her a toy. The mom pays for the groceries and angrily marches the kids out to the minivan. When she gets home, she's still fuming, and after sending the kids to their rooms to take a nap, she goes to an Internet support forum and vents about her son's "autistic meltdown" for the next half-hour or so.
All three people in this scenario lost their temper because they had trouble handling a stressful situation. The autistic kid hadn't yet developed the coping skills needed to deal with the sensory difficulties of the supermarket; his sister didn't know how to manage her frustration when she was not given the toy she wanted; and the mom got upset because of the noise the children were making and, perhaps, because of the embarrassment of being in a public place with two noisy children. But only the autistic kid was described as having a "meltdown."
I have used "meltdown" and "shutdown" both to attempt to describe emotional states that I do not believe many NTs have; specifically, I use "shutdown" (or, since my boyfriend started using it, "implosion") to refer to the semi-catatonic state I enter when depressed, depressed AND overloaded, or overloaded to the point of exhaustion. I use "meltdown" to refer to the acute stage of overload in which I become hypervigilant and agitated, when I still have sufficient mental and volitional wherewithal to try to escape the overloading situation. (More often, I simply use "overloaded" to refer to both stages, but I have used both of the words ABFH denounces as counterproductive).
Her posts have led me to reconsider that policy. At least on this blog, where one of my aims is to describe, precisely, vividly and coherently, my experiences with autism for use as a lens for critiquing others' writing about autism, I have decided that those words, by virtue of being jargon, obscure more than they illuminate. They're a shortcut. You might, in conversation with one who already knows you well, mention having a "meltdown" and expect them to know what that entails, but on the Internet everyone brings their own definition to the table. To counter this, I choose to be detailed and explicit. That's got as much to do with my conception of what this blog is as it has with any overarching political idea (Ballastexistenz in the comments on those posts made a good case for the use of those terms as a feature of online autistic culture, and as a genuine effort by autistics to define and characterize their own experiences).