You know what demoralizes a team like nothing else? And endless litany of projects that failed because nobody wanted to listen to the people pointing out problems.
When people on the team think they are pointing out problems, but are doing so without support, by simply saying "That won't work" instead of "That won't work because of ...".
This does nothing to further a project and leaves the burden of proof for a working solution on the person who proposed the solution in the first place, and the way for them to prove their solution is to continue working on it, with no actionable feedback to revise their project on.