This sort of thing has been going on since well before the internet. J. K. Galbraith wrote about how, during McCarthy's red scare, one had to put all sorts of caveats in parenthetical phrases to break up anything that might be quoted out of context (it still would be, but one could at least point out the elided text.) This was hardly new then - see Cardinal Richelieu's well-known epigram "If you give me six lines written by the hand of the most honest of men, I will find something in them which will hang him." It is probably as old as language.

If there is anything new here, the internet and talk radio has shown a lot of people how to do this. Some of them mistake it for wisdom, and others just like to annoy people who hold nuanced views. Don't blame the victims for the fact that it is no longer possible to assume anything reasonable is implicit.