As for the meaning of the disputed use of literally: I’ve been mulling this over, since it’s not trivial to analyze what’s going on.
Some notation for clarity:
literally(1) for the meaning in “He took her comments literally”
literally(2) for the meaning in “That is literally the meanest thing anyone has ever said”
On the one hand, wolfpup’s tome of argumentation notwithstanding, it’s quite evident that
literally(2) is not opposite in meaning to literally(1). It is used to add emphasis, but it’s not a straightforward intensifier, and it’s used mostly with metaphors. So what’s going on?
Consider a typical example:
It was as though she glowed.
In a simile, the comparison is explicit.
She glowed.
A metaphor makes a superficially false statement. Perhaps by conjuring the thought of somebody literally(1) glowing, the imagery is rendered more powerful. But, of course, it’s not really intended to deceive, the “as though” of the simile is implicit and very obvious.
She literally(2) glowed.
What’s going on here? It seems to me that this is just using the same “trick” of a metaphor, just taken up one level. Thus:
Simile = Here’s some imagery
Metaphor = This imagery is not a simile, it’s really happening! (but not really)
Literally(2)+Metaphor = This imagery is not even a metaphor it’s really happening! (but not really)
A metaphor, is a “lie” to intensify the imagery. Adding literally(2)+metaphor just takes the “lie” to the next level, it doubles down precisely because it uses the very word that we would normally use to try to discern whether a metaphor is really a lie. It’s a meta-metaphor.
Stylistically, is this a bad thing?
Well, metaphors are full of fantastic lies, and nobody wants to ban them! Literally(1) used to be the “safe word”, so that when getting a little bit experimental with metaphors, we always knew that we could make them stop if we became uncomfortable.
Will this result in hundreds of people being thrown in swimming pools because they are literally glowing? I doubt it.