I am the Kat that Walks By Itself

the attitudes displayed towards those native English speakers who showed support were enough to make me want to have nothing to do with it

Yes, there was one person - make that three people - there who... made me cry.

But the idea of fighting exclusion with more exclusion is anathema to me

But it isn't exclusion, it's accuracy.
I had originally thought that the idea was "post in non-English languages!" - in which case, excluding English-speakers would be exclusion, yes.
However, the fest isn't actually about that. It's about "post in your native language which isn't English!" -- because they want to be able to demonstrate how many people feel gagged by the dominance of English on the net.

Thus my offer to post bad-grammar German with Google Translate was perceived as an arrogant, thoughtless insult. And I understand why. No matter that I "meant well", I "did ill".