In my experience as a Dev Manager the easiest way to solve this is to put the expectation for coming up with a solution on the interjector or negative person. T

In my experience as a Dev Manager the easiest way to solve this is to put the expectation for coming up with a solution on the interjector or negative person. This is super effective in filtering the passionate contrarians from the the generally negative because it requires the person to do work, and the default to "no" people rarely will take on the responsibility.