I know exactly what you are talking about.

My approach would be.

“I don’t completely agree with this decision, but the people way up there need to make decisions based on all sorts of criteria we aren’t even aware of... and we need to make it work. Saying ‘they shouldn’t have made that decision’ is a waste of time, so we need to say ‘what can we do to make this work’.”

Think of it as a challenge. How can you make the process succeed in spite of the decisions you disagree with.

I’ve been working in a bureaucratic environment for 20 years and I’ve always respected my managers that were honest like that and I’ve always been honest like that to my staff. I have no patience for people who pretend something is a good idea when it isn’t. I either consider them stupid for not seeing the problem or spineless for not speaking the truth.

Of course it is possible that it isn’t a bad idea after all and I just need more context. So you do need to be humble enough to accept that you might not grasp the big picture.