There's more in 2 brains than in 1. So, you can (and always should) listen to anyone willing to improve for group's sake. Do you have to stick to what they unilaterally decide? I don't think so...
What I always did (and still do) when I was facing such a issue, was:
- Have a scheduled meeting with all the points that were to be discussed / disputed.
- Send a reminder to everyone involved, and ask for suggestion.
- Stick to the set agenda for the meeting.
- Go around the table, asking everyone if they have something to say.
This way, you have time to prepare and finalise the points and the report. It helps the group, as every person involved has a chance to intervene and explain their POV.
When the meeting start, a quick reminder of the points and schedule is important. This way, people will know they can't move around, and dilute or go off track.
Then, you can discuss every point. I really recommend that you first listen to what this naysayer has to say, and want to do. When you know what's good and what's not (take notes while they're speaking), you can challenge what has just been said.
Stick to the facts. Nothing personal. Make it business matters.
- Point #1: helps having more people involved, and a frame for the meeting.
- Point #2: helps having more suggestions and pros-and-cons before.
- Point #3: prevents from having off-topic matters and (often) rants.
- Point #4: strenghten the needs for everyone to be part of the group and talk.
If the "loudest voice" gives great advice, take it! If not, your counter-arguments have to be better than his. If you need a leader for this particular group, he'll stand up by himself because of its added value to the group, not because of its loudest tone :)
Finally, the last round of the table: you ask everyone their opinion about the best way to handle every point you've just discussed. A meeting is like democracy, it needs a frame, some talks, and some "leaders", people who will first organize, work, think... Whatever is good for the group, at the moment. But all have to be involved. And the group needs to use each individual strength and qualities for the group's sake.
Navigating TheWorkplace.SE, I found this related topic: how to handle the situations where talkative colleague dominates.
Side note: in a meeting, I often saw people not being part of the discussion all of a sudden talk and make a decision! How and why? Because when the "big mouth" had just ended, you go around the table and just ask: who is taking that part? wants to write this part of the code? If they don't like the idea, then, finally, they'll speak up, because they don't like the idea and don't want to do it the way the "big mouth" said it would be...