you bring up a good point. what matters is the forum where decisions are made. you can talk about ideas in private. but the ideas need to be brought up in the group before any decisions are influenced. especially if the private conversation is with a team leader. if a team leader hears an idea in a private conversation they should ask that person to repeat the idea in public. but also they should discourage team members to specifically approach them to bring ideas. that is what is meant by discouraging private conversations. of course you can talk in private, but if the idea is not repeated in public then it is as if it was never talked about