Difficulty of management of meeting with attendee from various companies

If all the attendee are from the same company, it is easy to manage the meeting.
Sharing backgrounds, follow organizational culture, lead conclusion.

But, attendee are from various companies, I can not force to follow our culture.
Some attendee insists his/her opinion with large voice.

Today, I met this situation. No one likes him, but he seems not to mention it at all.