You're talking like they're acting out based on some unrelated or irrelevant thing - as if they're taking a stand against Elon Musk's stance on trans people or his rather unique ideas about what "free speech" is. The unions are acting against Tesla out of their own self-interest - Tesla do not want to collectively bargain with a union. This is not something these unions are OK with and allowing it to continue unopposed could set a precedent that threatens their members and the conditions they've fought for.

In a sense these unions do have a lot of power when all of their interests align. But because of the sheer number of people and diversity of their industries and the political capital they expend in performing these actions, they don't tend to act at this scale very often. You need to have fucked up pretty badly to have mobilised all of these people against you.