Everyone identified as being on the autistic spectrum will at some point hear someone say something along the lines of ‘Right, but everyone is on the autistic spectrum somewhere, aren’t they?’
And that’s okay, as far as it goes. It’s mostly okay. Everyone wants to find common ground with people they’re talking to; communication and empathy always require a certain amount of common ground. Fun fact: this seems to be the main point of small talk. I always wondered about that. Anyway, there is a danger in overemphasising how different autistic experiences are, and things like sensory overload and meltdown are familiar to a degree to many people who are really not autistic.
And yes, while it’s important to realise that autism is multidimensional, it’s probably true, in a sense, that everyone is on a spectrum relating to autism. There is no clear cut-off line, and some people are much closer to autistic than others (often including family members of autistic people). But only about 1% of the population is in the part of that spectrum that is referred to as ‘autistic’, and that’s important. It’s like how everyone has a height, so sure, we’re all on a gradient that runs from really tiny to towering, but you wouldn’t say ‘everyone’s a bit tall’ or ‘we’re all on the tallness spectrum’, would you?
People in the diagnosable zone of the autistic spectrum generally have experiences that go way beyond what people outside of it experience, in frequency and intensity. That’s why it’s a thing; it’s useful having a label for people who share these experiences and tendencies, whether or not they’re understood in medical terms. For most of us who qualify as autistic, these tendencies can be seriously disabling at times.
So when allistics (non-autistics) say things like ‘we’re all on the spectrum’ or even ‘ooh yes, I know exactly what you mean’, it can sound like you’re not just finding common ground, but dismissing what makes us different, and the difficulties that come with it. You might not mean ‘we’re all on the spectrum, so why do you find this so difficult?’ or ‘we’re all on the spectrum, so why should I even take this into account?’ but you should be aware that sometimes, it comes across that way. By all means, find common ground — we’re all humans, right? — just try to be open to the possibility there might be less of it than you imagine.