Imagine if I'd written something about tides, and begun with a metaphor about swinging a condom full of liquid on the end of a string. No doubt some Christian fundamentalists would be so offended at that point that they'd stop reading and write angry blog posts about how "distasteful" it was to compare God's Earth to a condom. Would that be my fault?
You have to draw the line somewhere. If you write about things that are difficult and/or controversial, some people will misunderstand you. I try hard to write as clearly as I can, but the things you'd have to do to make an essay proof against readers who were really stupid or personally oversensitive about some topic would ruin it for the other readers.
If noone hates what you are writing, it is probably boring.
P.S.: The role of metaphor isn't to build an argument. It's to make it more vivid and easier to understand. (Bad writers use metaphors to try to build arguments, but PG didn't in this essay.) So even if the lion metaphor was a bad one (according to whatever criteria), that doesn't justify misinterpretation of the actual argument.
Absolutely. If you want people to take you literally, don't use metaphors.
If, however, you want people to think about what you're saying and draw inferences... well, go ahead and use metaphors, but be prepared to deal with people misunderstanding what you intended to say (and have someone read over what you've written to look for anything which could be particularly badly misinterpreted).
If you want people to read what you say literally instead of drawing inferences, don't use metaphors.
Seeing those guys on their scavenger hunt was like seeing lions in a zoo after spending several years watching them in the wild.
Do you mean that these scavenger hunters were pacing around and growling? Of course not -- you expect us, as readers who understand the nuances of English, to understand that this is a metaphor; to think about the differences between caged and uncaged lions; and to project those differences onto humans.
Guess what? Metaphors are imprecise. Different people have different notions concerning how caged and uncaged lions differ. Different people will project these properties onto humans in different ways.
I agree entirely with what you're saying in the essay, but I think it might have been far more effective if one of your proof-readers had said "you know, this is liable to be misinterpreted, maybe you can reword it?"