To know that such and such a language or framework is the most widely used and therefore the best, or any other unfounded position or debate. Once a developer has reached maturity, he knows which tool to choose for the right job. There's no point in fighting and debating. As a developer, we live in a galaxy of technologies, with an endless range of good and bad solutions for every use case. Taking sides isn't the solution, and it locks us into a box.
Let people use what they want.
What do you think?