Counterpoint: explain to me how to make two different versions of an app cohabit. I found out about homebrew, so it isn't as much as an issue as it used to be, but in the 2000s, it was impossible to maintain two versions of RoR on mac. Granted, window was not much better (two versions of crypt on ISS took me way too long to install correctly). But for anyone used to sane OS, it was a detriment until homebrew became ubiquitous.