People think the MEAN stack (MongoDB, Express.js, AngularJS, and Node.js) is a good idea because it allows for full-stack JavaScript development, meaning that the same language can be used on the front-end and back-end of a web application. This can make development faster and more efficient because developers only need to know one language, and it can also make it easier to transfer data between the front-end and back end. Additionally, the technologies used in the MEAN stack are open-source and actively maintained, which means that they are widely supported and have a large community of developers contributing to them.