Captain has to set the tone of the cockpit
One of the major roles of a Captain of a multi-crew operation is to "set the tone" - and the best way he can do that is in the flight planning area, when he first meets his crew. He must encourage participation in the entire flight process. If he is normally a miserable downbeat so and so then he probably should not be on duty, and needs to talk to a professional. Depression is a mounting factor in pilot medical issues - huge number I heard in a professional briefing last month. To be dour and non-communicative will discourage others from speaking up on anything, perhaps to their detriment - plenty of accidents on record where the crew atmosphere was a factor. This doesn't mean you have to be on some sort of manic high with a motor mouth - just set a quiet professional tone and openly state your goals for the operation. Let your fellow pilots know that you value their opinions. If you don't want too much BS'ing - let them know that up front too. i..e save the bitching and moaning for the bar. Upbeat converstaions only in the cockpit!
It's up to Mr. P1 - if he/she has the communication skills of a dog !!!!, that will roll over to the rest of the crew - and then you are in big trouble.