Do you think they really want to help people or is it more likely they are trying to get ahead of being broken up or overtaken by a government appointed authority
I'll probably weight that warning as "might be ml interesting". Seeing that what I like (the old Web) is dying a slow death under the weight of modern privatised censorship, what they're marking as bad might become signal, of sorts.
And the first, relatively mild warnings on cigarette packages probably didn't convince many to quit, nor did posting calorie counts on fast food menus make everyone switch to salads. But hopefully it's the start of a drumbeat where this type of content becomes less and less acceptable in society.
It's not the perfect analogy of course, but I think the solution to divisive, negative, nasty online content is largely a social one not a technological one.
I don't know anybody who trusts facebook (the company).
But I do know a few people who are all to eager to trust everything that gets posted on facebook, and a sizable chunk of these people would indeed take such an "extremist warning" by facebook to mean that "they" are trying to hide things from the public.
All of my right-wing friends and acquaintances who received this message mocked it and took it as more evidence of Facebook's bias, so I'd say it was inversely effective.
I see it more as a way of nudging, herding the cattle so to speak, to get people thinking in the way that big tech wants and finds useful.
This is not the same thing as discouraging extremism.
By any measure, the invasion and monetisng of peoples privacy like Facebook do is extreme.