With your DH, there are many reasons why he might not be on board. I believe with Autism there is some links to it being hereditary, is it possible that your DH may also have some characteristics, which may be part of the reason he is responding how he is?
Spot on. He has spent his life unable to relate to social situations, and alienating people due to his black and white views. When our eldest DS was diagnosed with ASD we were astounded at how ASD signs aligned with DH's behaviour. However, at this point any diagnosis for him would be irrelevant and I'm always a bit wary of people who self-diagnose themselves with ASD. Drives me crazy.
That is certainly part of it. I think with the ODD side of things DH thinks that well, he got through it so it's not insurmountable and doesn't require intensive intervention. What he doesn't realise is that ODD goes far beyond what he has experienced.