Why was Rabbi Eliezer ostracized?
The context here is the aftermath of the debate about the oven of Akhnai.
What did Rabbi Eliezer do that was worthy of ostracism?
Dissent, by itself, must have happened many times without disciplinary action.
Was he considered to have broken the rules (using reason to settle legal questions) by asking for miracles? But he had started with reasoned arguments, many of them. Their substance is not recorded but assumptions can be made based on his career and reputation.
Dissent can take the form "I disagree, but acknowledge that I'm outvoted and won't fight the decision". What did Rabbi Eliezer do that went beyond that? I'd understand the Sanhedrin finding a serious problem if, hypothetically, a rabbi were to teach students and the public that something was ritually pure when the Sanhedrin had ruled it was impure. But I haven't seen anything at all close to that in the few sources I've read.
Certainly praying for bad things to happen to the Sanhedrin was outside the bounds of normal dissent, but didn't that happen after he was ostracized?
Was it a straw that broke the camel's back situation? Did I get the correct impression that it was not the first time he was a minority of one?