Frameworks and libraries are tools of our trade. The reason to use them or not to use them depends on the context. While it is foolish to become a 'Backbone specialist' and look at every project with those eyes; it is equally foolish to dismiss frameworks as prototyping tools.

Lots of frameworks interoperate well and are amenable to customisations. The good ones are more than sufficient for most client needs, even for prolonged production usage.

Most open source frameworks are results of thousands of man-hours of effort by specialists from different backgrounds. Many aspects like security, modularity and functionality are examined by hundreds of eyes. It is perhaps naive to assume that one's knowledge of the domain is so good that they can roll out their own framework much better than what anyone else has produced.

In fact, if that person is so capable, they should be encouraged to post their code for a public review and help others (or possibly be severely critiqued for their questionable design choices).