The introduction of CRM courses made a big difference in helping inexperienced co-pilots challenge any odd decisions made by the captain. It gave them confidence because they knew the system would back them up and also demonstrated to the "crusty" older captains that they could and would be challenged if they "did their own thing".
Doesn't seem to working that way. I'm sure the vast majority of co-pilots may say something, but the numbers that remain insistent and who will physically intervene probably drop off exponentially as the amount of effort required increases. Sim instructors feel free to chip in here: do you see a lot of cases of the PM verbally intervening initially when things are going sideways, but who subsequently desist?