The article in the DailyMail did not suggest causation. They simply quoted statistics from another source.
Then why is this a news worth telling, and why did you laughed and posted it here?
You laughed, it means you found that funny and worth citing.
Why is it worth citing and laughing if people still live with their parents?
Because you think that people who live with their parents are losers
And the fact that so many left radicals live with their families makes you laugh because now those people you already despise are, in your brain, shown to be losers.
This means that you thought that the correlation between them living with their parents and them being left radicals was actually a cause, meaning that you can't be a left radicals if you are not living with your parents, or, to say it clearer, that you can't be a left radical without being a loser.
And this is also why that piece of news was so interesting for the Daily Mail (provided, of course, that the data shown is true, since we are speaking of the Daily Mail).
Except, as I told you, it is not at all strange to find most anti-system among those people which are not successful in that system.
This assumption also has a far, far stronger connection to the data, because it is quite more simple to say that people are anti-system when they feel rejected by it (for whatever reason, even being a loser) than it is to say that they are anti-system because they are losers, and that their being losers is shown by the fact that they are not well integrated by the system.
That's a simple use of the Occam's razor. Your way of thinking is exagerately more convoluted and complicated than other explanations.
I've never heard that anyone make that claim. Got a source that doesn't involve the KKK or something?
Why?, that was taken out of racist propaganda for the specific purpose to show you how the same fallacy is used by despicable people to fuel their hate. I'd say it worked a charm.