I admit, I'm slightly put off by labelling people.
If you go to the hospital with an aching abdomen and they diagnose you with appendicitus, they've provided you with more information and have genuinely helped you to get treatment, as they've identified the cause. If you're having trouble socialising and recognising social cues, and they tell you you've got autism, well... what exactly does that mean? It means that the range of problems you have which you already knew about puts you into
this arbitrary group of people who act similarly. It's not the cause, it's just a classification of the result. It feels like going to the hospital with an aching abdomen and being told you have "Strange Aching Abdomen Syndrome".
There is some use to it, but not in a diagnostic way, in my opinion. It's more like categorization - putting you into a group where you might be able to get stuff better tailored to you.
By the way, there's been debates over whether HFA and AS should be merged, because ultimately the results tend to be just about the same.
I think the distinction you're trying to make is between LFA and HFA--and you're right that it's a very, very big one. One of the reasons why I'm antsy about even considering having children.
I dunno, is there evidence to show it's heritable? Unless you're more worried about upbringing, I guess.