Ignoring sounds passive but there is nothing passive about telling people their ideas and cooperation is unproductive (be it people from product, RnD, management, QA etc), you spend much time and energy convincing them their ideas are not concrete, or are going in a bad direction, or are simply bad..
Having the burden of completing the project (successfully!) on me, I have to cut through the BS and provide results, not attend to egos and fragility of everyone involved..
Never the less, I try to be dry and not personal as I can to communicate the situation as simple as possible to the other party..
In my consulting career I learned that being "nice" is not worth it and ends up costing me in mental health..