How do you defend the messaging that you’ve created when everyone in our company has an opinion about messaging.

I'll take a more extreme position on this question. You're setting yourself up for failure by asking us how to "defend" your messaging. Instead, I'd ask you to listen to those people who you are used to "defending" your messaging from. It's not your messaging - give up that pride of ownership in order to listen and learn from sales, product, and your executives if they choose to care about your exact phrasing. That doesn't mean that they get to write the exact words - but all of those constituencies have an important point of view, and it's your job to triangulate among them, decide where to give weight, and come up with messaging that is clear and compelling. When you think you totally have that message nailed, you're not finished. You're at step 1. Next, you need to test that messaging with real, live customers. Don't look just for confirmation of your message - lean into those people you interview who find your amazing messaging confusing or bland. Figure out how to make it right. This is an involved process, but it's amazingly powerful. Then, by the way, when someone comes and says "hey that message isn't that great, how about XYZ" you can say "well, we crafted this message with your input and the input of other leaders, then we shared it with customers and made ABC changes based on their feedback, and this is where we landed." 

Everyone having a natural gift for messaging is an amazing coincidence, indeed :) Per "ways of testing question", the best approach is backing your messaging with methodical research that shows validation by customers, prospects and industry analysts/influencers. You still need to do your homework about competitive messaging and gather feedback internally from sales / field folks in particular. But formulate hypothesis / draft messaging (and gather internal feedback for that) then do your research per above, giving read outs but not keeping the blue-sky ideation phase going indefinitely, then defend it based on the merits of your findings and your synthesis as a PMM.

I’ve never met a PMM who was able to keep everyone happy. So I’d reframe away from that goal as much as possible. Instead, I like to focus on how to keep your messaging defensible early and often.

You’re right that everyone has opinions. But there are a few opinions that matter most:

• Customers and prospects: They are the lifeblood of your business.
• CEO (or business GM/leader): They own the company strategy and where you’re going next.

There is no better defense than real evidence that your messaging reflects how customers and prospects talk about their pains, their desired outcomes, and the product they want to buy. At the end of the day, this is what most internal teams are looking for. Sales want to say what these folks want to hear. Product wants to build what these folks want to buy.

You’ll notice that I jumped straight to the highest-ranking leader as the other priority. At the end of the day, I found that your messaging will never stick if you don’t have a champion in your leadership team. While the customer proof points serve to give you a bottoms-up defense, your leader can be the top-down champion that you need to keep stay the course and avoid getting drowned in opinions.

Finally, be open to people’s feedback. When they feel heard, when you connect what they’ve shared with what others have, they feel considered and included. And over time, this will lead to more champions and also a few nuggets of actually great feedback.

200%. The way that, when necessary, I defend messaging is with customer feedback and validation. For example, with our website copy and billboard - I got some push back that it wouldn't really resonate. So I scheduled some sessions with customers to get their feedback. With that in hand, it was a lot easier to defend my positioning - since what the others had was just a feeling that it wasn't right, while I had names and quotes about why it was. 

But ultimately, I, and the rest of the team, tries to adopt a test and learn mentality. So we try not to over invest mentally or emotionally in my messaging. Let's try it out, see how it goes, and be open to change quickly. That attitude makes 'defending' less likely to be necessary or happen.