I can definitely see where you're coming from, Cleander, and honestly, I'd never thought of Eustace in this light before.
My first introduction to his character was in the BBC version of the film (which I watched prior to reading the book.) as such, David Thwaites will ALWAYS be Eustace in my book. He really brought that character to life for me, and did such an amazing job at portraying a character that one automatically disliked. Thwaites did such a fantastic job, that when I did finally get around to reading VODT for the first time, I found "book Eustace" to be a bit more tame than "Thwaites Eustace" even though we get more instances of him whinging and complaining in the book than we do in the BBC adaptation.
I feel like all of us know people like Eustace. People who, no matter what you've done, they've done it twice. No matter what you own, they own something nicer. No matter what you do, they've done better. Such people also refuse to be wrong under any circumstances. These people are a part of our lives, and while we may not "dislike" them as people or as individuals, everybody who knows somebody like this will say that they are an emotional drain to be around.
I think the point of him being a vegetarian is not because he has an objection to eating meat, but rather because it shows him to have better self control than his peers. His family doesn't drink, not on religious grounds, but rather that they have something over which they can feel superior. They are pacifists not because they disagree with the horrors of war, but because they dislike the self sacrifice that comes along with one's country being embroiled in a war (think rationing of commodities, loud noises interrupting one's sleep, etc....)
Part of Eustace's transformation personally definitely has to do with stripping away these things. We see him eating meat (the carcass of a dead dragon) violating his vegetarianism. We see him rather non-pacifistically slaughter the native wild pigs of Dragon Island and giving them as provisions for the ship. When he is brought to his lowest point, he realizes that he has no need to put on these airs any longer. . . He is quite literally the "least of these" so to speak. Subhuman. An animal. And that experience humbles him, and changes that mindset in his life.
From that point on, I think we see such a change in Eustace, not because Aslan spiritually changed him, or because he has had some great revelation, but rather because he saw that he was accepted, and cared for by those around him, even when he didn't have the ability to put on the airs that he had done so his entire life. It is this new found freedom, this liberation to be one's own self, that allows him to learn all of the other things that he does (kindness, a relationship with Aslan, sharing, basic human decency, etc...)
And as the books progress, we see Eustace getting stripped away more and more of what society has made him (think early in The Silver Chair, where we see how his relationship with bullies has changed since his adventures in Dawn Treader) and more and more of an individual.
This is classic Lewis theology. . . in that as we strip away more and more of the things that we think make us better than others, we become closer and closer to God, and as a result, become more ourselves than ever before.
So in the end, I think it's okay to dislike Eustace. I think it's okay to sympathize with him and feel sorry for him to an extent. We can all identify with the fact that we have certain expectations for our lives, and that when said expectations fall short, it is frustrating. We all complain. We all put on airs for those around us. It is only when we lose those things, and are stripped down through an encounter with Christ, that we become truly ourselves. (Although, like post-conversion Eustace, we still have moments when we are, as Lewis puts it, "Very Tiresome"
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