Some people still don't want to hear that their idea sucks, even in private.

I don't get why people are so attracted to this idea that the manager is the only party with any agency or ability to influence outcomes, while underlings are merely mechanical cogs to be properly organized by appropriate managerial incantations and social engineering.

As an underling it's great to be responsible for nothing negative, but this also means you don't really deserve much credit for the positives. Managers might throw false praise your way to manipulate you - as per your suggestion - but who cares about that?