I'm a PM at Microsoft and this post hits close to home. I think there are a good number of PMs that you're talking about. It's easy for the PM role to evolve into pure politics because our job is to represent the customer. Just like our government's politicians sometimes claim to represent the people and end up making selfish decisions, PMs aren't immune from that weakness. The role attracts people who are good at politics, so you tend to see a high concentration there.

Why do I still do the role? Well, it kind of fits what I wanted to do for a living. I always enjoyed doing lots of diversity in my job and trying all kinds of new technologies out. I get to be a customer for a living. I try out our product and think about where I want it to go. I can be annoying (a real customer would probably be a bit annoying sometimes too, they challenge your product and your hard worked design). I get to care for a living. As an engineer, I could see myself needing to let things go because it's gotta get out the door. As a PM, I know a customer is going to hit that issue and I need to get it in front of people so we can fix it. I'm building applications using our technology and competitors and technology not obviously related just to see if could be relevant.

The problems with PMs vs Engineers is that it is super hard to tell a good PM from a bad PM who is good at politics; but I'm still super happy the role exists. I'd likely have to become an evangelist to do the things I do everyday still, but I'd have less influence with the engineers and it'd often be reactive if I wasn't on the product team. To any people considering a job as a PM, do me and your other future customers a favor and ask if you can care more about your customer than having your job or being promoted? I've held fast to the notion that customers are why I'm here and my career hasn't been too bad so far, management still recognizes good work with customers. But if it all goes to hell, I can always find some other job and be happy with myself.