>How is modularization and code reuse a bad thing?

The problem he is complaining about sounds like a lack of modularity to me: being forced to pull in dependencies that he won't be using at all.

He's using hash tables, so he's using glib2, and that's far better than everyone implementing their own hash table.

False dichotomy. Libraries that provide basic data structures should not have external dependencies. The issue isn't whether or not to use libraries, it is how the functionality of the libraries is organised.