A legal practice which increases competition and increases the allocation of resources to productive individuals can't be compared to an illegal practice which decreases competition.
I do not think it's ethical to scare the other party by threatening actions that you have zero intention of carrying out.
Regardless of your opinions about the morality of this practice, there's no basis for calling it collusion.
It's not to say that all engineers were doing it (which I think is a salient point), but in all these arguments, the engineers are painted as naifs who had done nothing as a group to merit this. To be clear, I don't agree with the ethics the companies displayed, I just think it's unfair that the collusion between some engineers gets glossed over amongst all the outrage.
I'm sure there will be apologetics, but it's not like one side was behaving ethically.
They conspire illegally to drive down wages, then whine that not enough people want to work in this field where wages have been artificially and illegally deflated.
This field where wages are still significantly above mean values? Where are these engineers going to go en masse for better wages? Into medicine? Hello for another 10 years training. Law? Already overstaffed, and wages are similar for most anyway. Finance gets some, but isn't going to hold them all. If the engineers are in the career for the dollar, restarting in another career that will pay more is going to be difficult as a group.