Why try to be a clown when everyone already know you are a full blown troll. Educate yourself.
The mangled form “for all intensive purposes” has been “spotted in the wild” in print (and noted by linguists) at least since the 1980s, although, as an error in speech, it may have been around much longer. “For all intensive purposes” is a classic “eggcorn,” a re-shaping of a word or phrase that, far from being a simple error, has flourished and persisted because it actually makes a certain amount of sense. The term “eggcorn” itself was coined in 2003 by linguist Geoffrey Pullum when someone online was noticed typing “eggcorn” instead of “acorn.” It was, of course, an error, but an acorn is indeed rather egg-shaped, and is a seed, as is corn, so if one has heard “acorn,” but never seen the word in print, writing it as “eggcorn” is not entirely crazy.
Similarly, “for all intensive purposes” might be defended as logical if “intensive” were interpreted to mean “serious, realistic, or practical,” making the phrase equivalent to “when push comes to shove” (“Smith is a decent hitter, but for all intensive purposes, he’ll be useless in the playoffs”). It’s still “wrong” in that it mangles a long-established English idiom, but it’s not as far off the beam as “The ants are my friends, they’re blowin’ in the wind” or “There’s a bathroom on the right.”
As to how “intensive purposes” crept into common usage, I think it’s significant that the 1980s also saw the proliferation of “intensive care units” in hospitals and the ensuing use of “intensive” to sell everything from skin lotion to motor oil. Given that “intents and purposes” has a distinctly archaic ring to it, and that “intents” is more rarely used than “aims” or “goals” today, and “intensive” seems like a logical interpretation to folks who have only heard (and never read) the proper form of the phrase.
Intensive Purposes « The Word Detective