It's terrible hot take time:

React is capitalist. Since it's been ported to many platforms (browsers, node.js, iOS, Android, now even Sketch) it is designed to let businesses reach customers on all platforms with less development effort, instead of hand-crafting apps that care about each individual platform's users. And there's a sort of lock-in, you're not a web/iOS/Android developer, you're a React developer. That's kinda like businesses trying to lock you in to their ecosystems (Apple, Microsoft).

In contrast, Polymer is good and communist fully embraces the web as the only platform, which is good for the open web.