We know they reacted in a way which forced OP to go to his manager.
>Or maybe, based on the alleged jerk’s aggressive behaviour to the team in the past
If that were the case OP would have mentioned it. Workplace bullying is certainly more important than disagreeing and this would make a reasonable case to fire him. If the jerk was bullying his team and OP did not notice, that would prove my argument even more.
>Or maybe they’re junior.
There are 9 other people. And they weren't asked to stand up for their own opinion, but for their team leads opinion. I do not think this matters much. 9 people not standing up for you as a team lead is a very bad sign, even if they are all juniors.
>Or maybe you’re right and all 9 people unanimously felt OP was in the wrong.
This isn't my interpretation at all. My interpretation is that OP had one opinion the other guy had his and the rest did not particularly care either way.
>Criticise the reported actions, sure, discuss some hypotheticals, but going straight for “you’re a bad leader” goes a bit beyond.
But having to go through your manager to force through a totally reasonable decision that is yours to make is being a bad leader. I do not think that there is any alternative interpretation then that this event at least is a failure in leadership.
I am saying this because I want to tell OP how his situation sounds to a complete outsider. OP was there if the 9 guys all immediately stood up for him and told the other guy that he was clearly in the wrong, then this obviously disproves everything I said and OP knows that I am wrong. But if they did not, then he should reconsider his actions and at least allow for the possibility that this was a failure on part of his leadership.