Comment by o_nate

Inheritance is not necessary, but then very few programming constructs are absolutely necessary. The question is does it help program clarity or not. I think that in some cases, used sparingly, it can. The main danger of inheritance is not that it is OO, but that it is not OO enough. It breaks encapsulation by mixing properties and methods between base classes and derived classes without clear boundaries. Composition is safer because it preserves encapsulation. In general, I think that protected abstract methods are a code smell, because they usually indicate close coupling of details that should be kept separate between the base and derived classes. But used correctly, inheritance can be more succinct and convenient.