@anonhop we might be violently agreeing, but I don't think so.
Your post gives the impression (perhaps unintentionally) that "SEN" and "NT" children can and should be conveniently stratified, and that the interests of the NT kids should always pip those of the SEN when push comes to shove. When it comes to - say - school trips or other opportunities, there are laws in place to protect disabled people from attitudes like this, and they require reasonable adjustments to be made by schools in these scenarios, without exception. Those laws are required precisely because people invariably take the path of least resistance, and it's more convenient for everyone if the SEN kids are not accommodated. As a mother whose autistic child would have been prevented from participating in many activities while in mainstream had I not been extremely vocal about the requirements of the 2010 Equalities Act, I know exactly what "if it can be facilitated without negatively impacting the NT children" means in reality - it means the autistic/ND children are left out in every case and experience further disadvantage compared to their peers, while every other pupil has a jolly nice time. That's not a good look either.
As for "risks to physical safety" as a result of inclusion, could you clutch your pearls any tighter? My autistic child struggles massively with regulation and can lash out at others (as can many primary-aged children without ND), but somehow buggered along in mainstream for two years without damaging anyone. He had to really, because the LA weren't in any hurry to place him elsewhere. Even in his current specialist setting, where pretty much every child has this profile (or worse), nobody has been "seriously affected" or "at risk" of violence. Yes, this requires well-trained staff who do their jobs properly and understand ND conditions - surely, this should be the goal well before we shove the ND kids out of the classroom? Would you exclude a primary-aged child in a wheelchair from PE because he was stopping the more able majority making decent progress in football? If not, what is it about ND conditions that makes you feel differently?
Your final paragraph is rather naïve. As a SEN parent who belongs to numerous support groups, no amount of "parents banding together" can give LA's the budgets to make a difference, even if the appetite and expertise was there (and in my experience, it isn't). Parents of disabled children have quite enough to contend with - not least the attitudes on display in this thread - but you want to put the onus on them to make things better, while preserving the status quo of inclusion only "where possible and beneficial for NT children" (fixed that for you).
Yes, I absolutely agree that specialist education should be better than it is. I am old enough to remember when virtually all maintained specialist schools were closed in the interests of inclusion (which was actually all about money, of course). For whatever reason, we have many multiples more SEN children now, and far fewer places to put them other than mainstream. Anecdotally, there was no suitable LA school/hub for my child's needs, but even if there had been, locally all specialist provision was full, often beyond capacity already. The only option was a specialist independent at a cost of £100k-ish a year for the next 12 years. Pointing out that the majority of SEN/ND children will HAVE to have their needs met in mainstream schools, with whatever adjustments may be required, is not a political or aspirational statement - it's fiscal reality.
Please don't "other" disabled children relative to their peers. The emphasis should be on making mainstream work for ALL children (including the 1/67-odd who are likely to be on the autistic spectrum), not nitpicking over if and when inclusion is acceptable to the NT/able majority.