I generally consider it rude to not use headphones in a meeting. The primary issue is you can't have simultaneous talking when someone isn't using headphones, s

I generally consider it rude to not use headphones in a meeting. The primary issue is you can't have simultaneous talking when someone isn't using headphones, since most applications auto-cancel audio input when they detect feedback. You then have to switch to turn-taking which isn't always suited for certain conversations.