I think 'disdain' is a sad word to use.
I feel sorry for them because frankly, there but for the grace of some deity (you choose) go I.
And I haven't always been LCHF. I just happen to have been lucky on 2 counts: I received the message, and I got the message.

It's unfair to consider such people 'unworthy' (that's the root etymological meaning of disdain - to deign people unworthy of attention or respect). Every human being who walks with us, has some good qualities; It's just a question of tapping into them and easing them out.

But I used to eat carbs. heckarooney, I loved them! If anyone had told me 10 years ago I'd want to cut them out of my life completely, I would have laughed in their faces.

Yet here I am: an Italian who doesn't eat pasta. A baker who won't touch bread. A Sushi-lover who shuns glutinous rice. A vegetable grower who has no room for potatoes or root veg.

But all these things, I have previously done with Molto gusto.

Do not cultivate disdain, for thereby you create separatism and hierarchy.

Don't judge.
Let the results speak for themselves.

I am not beyond using no-nonsense terminology. But only when challenged, and then, I 'tell-it-like-it-is'.

It can go like this:

So, what do you do?
It's what I DON'T do. And I DON'T eat any form of added carbs.
But you need carbs, right?
Nope. never have, don't now, and never will again.
I don't believe it.
Well, why ask me, then? If you don't want to take my word for it, please yourself, but at least back up your statement with research. I can give you links, if you want to read...
It's just a fad...
It's only a fad if it's temporary. I aim to make this permanent. And all it's done so far is keep me healthy and make me lose weight.
Well, I eat carbs...
How's that working for you?
I feel ok...
Well good for you! so do I! So, you do your thing, I'll do mine, and we'll compare notes further down the line, ok? Have another doughnut. Feel free...
Well, I can't have too many...
Why not?
Well, too much sugar/fat, is bad for you...
But you just said you feel ok...
Yeah, but I don't want to overdo it..
Let me let you into a secret. Even one doughnut is, strictly speaking, 'overdoing it'.
A little of what you fancy does you good...
Yeah. Carry on believing that. All this 'moderation' crap. Good luck with that.
Cutting carbs is what's good for me. Oh and, by the way, my H has dropped a stone, two trouser sizes and is off his diabetic meds completely. Just thought I'd mention that in passing.... *wink*
Wow! That IS good!
Yes. But according to your thought process, he should still be eating carbs. Which is what started him off on a diabetic downturn to begin with...

And at that point, they suddenly get more interested.... or walk away.
Because there's no answer to that....

So walk gently - but firmly - among those 'set in their ways.
They'll either get it, or they won't.
If they do, help.
If they don't, accept.