I think a big reason why it comes up so often is that it's rarely worth the mental real-estate to become proficient in both since they are so similar in design and problem domain.<p>There is significant diminished utility in learning python after knowing ruby or vice versa. You're better of learning something totally different (like haskell!) since you already have a flexible modern scripting language with a great web-framework in your toolkit.<p>However since each language has its trade offs, people have to keep convincing themselves (loudly and publicly, usually) that they made the right decision.<p>So basically, it's contentious and will always be that way for the same reasons that people still debate vim vs emacs after twenty years.