Mostly I agree with the people who say that language changes and that rabbiting on about proper or correct usage is pedantic and useless.
I love language, well, English. I love its magpie-ness, its amazing size, its idiocies.
English is capable of great precision. I don't know another language well enough to compare (somebody?), but think of its moods and tenses, dependent and independent clauses, huge vocabulary, incredibly flexible sentence structure. . .
The proper placement of 'only' in a sentence is one of these devices that increase precision. It is not difficult, it is logical, and it is extremely helpful to the reader. Properly done, it sharpens the sentence up. Improperly done, it drives me batty.