“But regarding the Brooklyn eruv, a psak was made by the preeminent gadol hador with the support of the overwhelming majority of other gedolim behind him.”
The same could be said here. Every major rabbi ever has asser’d going to church services. If anything, that’s a lot more to being going up against than just Reb Moshe alone.
“he defended himself with some teshuva he found, and they decided not to get rid of him.”
This is how the process should work. As you can see from this thread, the pro-church crowd thinks that explaining halachic reasoning is comparable to sharing nuclear secrets (but only when it’s a heter, of course). Occum’s razor is that the reason they aren’t making this whole controversy go away by just sharing their reasons, is that they have no real reasons. I would be happy to be proven wrong.
“But because I’m not very familiar with the british rabbinic scene”
From the rest of your post, you seem to be more familiar with the British scene than you are with the American one. The Brooklyn eruv was a project by chassidishe rabbis, including the Nitei Gavriel. Not unlike what you said about Britain, they “get along” with the greater frum tzibbur. However, unlike the case of Britain, they don’t turn around and support the gay agenda. Given your shittos, you would consider the Brooklyn rabbis abjectly more respectable than those in England, yet you’re more willing to criticize them.