>Eh, it's become acceptable, sure. It's the age old prescriptivist vs descriptivist debate. That same Merriam Webster link you posted also includes, e.g., a definition of "literally" as "figuratively" and our friend "in actuality".
The Oxford dictionary sported the secondary definition of the literally since 1903 -- the use is much older. After over a century of common use and lexicographic registration, I don't think it fits into the prescriptivist vs descriptivist debate anymore (that would hold for more modern mistakes, not century-old established language -- do those people also argue that "awesome" e.g. is something that inspires dread, as per the original meaning of awe?).
The Oxford dictionary sported the secondary definition of the literally since 1903 -- the use is much older. After over a century of common use and lexicographic registration, I don't think it fits into the prescriptivist vs descriptivist debate anymore (that would hold for more modern mistakes, not century-old established language -- do those people also argue that "awesome" e.g. is something that inspires dread, as per the original meaning of awe?).