If he raises the subject again, just laugh and tell him the 70's need him back.
We're a long way from those days, but the stigma of 'labelled' remains, and there is an unspoken 'contract' among mainstream school parents, that their choices in how a child should be educated is the only correct one and anyone seeking something different is 'breaking rank.'
They take it poorly. It's peculiar and often to do with their own insecurities around what they've chosen or had to settle for and sometimes a need for others to be under whatever levels their child/ren achieve.
Children with difficulties who aren't kicking off, are expected to drag along trying to overcome their issues themselves through 'inclusion' in unsuitable teaching and being around non disabled children. When they fail, the child's blamed not the unsuitable methods used. It's criminal tbh.
We'd already done the assessment, journey, Gt Ormond st NHS diagnosis journey, EHCP journey, then the rewriting of it to be meaningful, getting funding for a 1 to 1 to differentiate lessons, only to have the school hire someone with no interest in education (told Dc "I wipe bums and noses" when asked for help)
School wanted to focus on what Dc couldn't do, and not allow any progression until those basics were achieved. I knew that might take decades (it has, and many are still absent) if ever, and would leave low education and unbearable frustration. They wrote the line "And you're gaining your inclusion at the cost of my exclusion" and was spot on.
Dc went through hell and a lot of damage before I pulled them out of school where they were headed for ASDAN certs only.
Capable of passing several of them without educational input, so ticking a box for the schools stats. School was adamant that they were enough, and Dc needed to accept they'd always be bullied as 'different' and learn to minimize 'causes', by being around the bullies.
When school became truly dangerous and I pulled them, a PRU placement alongside some of the expelled bullies was suggested. Others were at least shocked at that, but even then suggested we should try it over home educating as 'LEA wouldn't suggest it if it wasn't in Dc's interests.' Hmm...
No school friends, so better they worked alongside those who tormented them, and everyone else kept their Dc's away from, than try anything different.
I should 'be normal' and accept what LEA and school were(n't) doing for them.
I did end up home educating and took the LEA to court for the funding they were now saving to aid it, and became almost everyone's pariah parent!
Everyone knew there 'was no choice' but to put up with what the LEA offered if you couldn't buy a house or fund private yourself. Doing it threw up the idea I was rejecting 'what everyone had to put up with' or their choices, in their heads.
I got accused of many things by people with no concept of the specific teaching and learning my Dc needed.
The judges turned out to be the only ones in agreement (all you need) and Dc went on to recover from the worst of the damage, (not all) make a big long term circle of friends, achieve high exam results, and went to Uni.
Covid changed their original direction and they are now a school senior technical tutor with a sideline in differentiating learning.
But they're a rare beast in MS schools and frequently come across disengaged students who've been basically failed throughout MS education, who clearly needed specialist help they never got, and now have to live with the results.
Do whatever will give your DD their best shot, ultimately others will get over it.