Bringing the smartest people into the same room rarely leads to successful, positive, outcomes. I can think of 5 reasons for this.
First, the people you’re approaching probably lack the diversity of experience and expertise to create a new outcome. You probably know the perspectives and views of the person you're approaching, or you wouldn't be approaching them. If you can’t solve the problem already, more of the same doesn’t help. Including more women is a major asset. You need people who have opinions/views you're not already familiar with.
Second, the group you’re approaching probably considers themselves smart. They’ve been praised for it many times. They have egos. They hate to admit they’re wrong. They hate being challenged by others. It leads to stubborn conflict. The group may comprise people who consider the other members their biggest rivals.
Third, people may be hesitant to challenge others if they have a vested interest in that individual's support in the future. They're equally worried about putting forth and opinion and being shot down by that group.
Fourth, the status quo supports the smart group, it helps them build and sustain their reputation. They will typically support ideas that maintain the status quo (i.e. their ideas). it's these ideas which are the cause of your problems in the first place.
Fifth, smart people really care about important things like group process and facilitation. How are opinions solicited, supported, and debated? Smart people only create smart opinions in smart groups that have smart processes.
I'm sure there are more.
Some things can help.
Submitting and debating ideas anonymously can useful. It frees everyone to support/criticise/debate them. Forcing people to support their points with evidence is also useful. It counteracts one loud person forcing their view upon the other. Addressing the concerns above can also help.