I am also one of those not well-informed on buggery.
If someone used it in a sentence to refer to a particular sex act, I'd really just think it was a crude way of referring to sex in general. I never knew it had that other kind of specific meaning.
There are two interpretations here:
1. Card is a learned writer who includes all kinds of layers of meaning, as writers are wont to do, and must have known what he was going in using that word.
2. Some people here are suffering from confirmation bias, assuming Card was making a sort of sly-as-a-Magic-Eye allusion to homosexuality because they think he's basically obsessed with the topic, when in it was really just a simple way for humans to term bug aliens.
As far as literary analysis goes, the first interpretation can make you feel smart because you're seeing through the layers. But it's also awfully lazy. The second interpretation may be criticized for being naive. I don't know the truth but I'm not going to assume ill intent in the use of the word "bugger" to refer to bug aliens.
All I can say is that I would never have made the connection. I've been doing a sort of personal study of Baum's Oz books. Some have argued that Baum was writing an allegory about the politics of his day, and while many colorful analogies can be drawn, it's still unfounded. I wonder if there may be an atheistic streak in Baum's writing, where the only life that matters is the one here in Kansas, however bleak and gray, rather than a fanciful world where one seeks salvation from a great being who actually isn't. And the only "salvation" that matters to our protagonist - to be back home - is obtained essentially by her rejection of that other world. The scarecrow had remarked that if people didn't have brains they'd probably all live in the beautiful places (unlike brainy Dorothy wanting to be in Kansas rather than Oz). There was also the sole bit of religion in any Oz book in which a china church steeple was broken by a swing of the lion's tail. On departing the china village, the heroes remarked that the village was unjustified in its anger since they only lost a church steeple and the hoof of a cow. Seemingly equating the two was curious to me.
Then again, these are just musings. I may be reading tea leaves. Maybe it is best to take Baum at his word that these are just fairy tales with no other real meaning.
I respect not buying something when you find the creator "evil" but it's getting nutty to be so certain that anything he wrote that might be construed a certain way must be construed that way.