I'm comparing to macports. I remember a brew update that removed an old version of openssl causing all of my older ruby packages to fail. Now I would definitely not use ruby 1.9.x in production but I sometimes do have to be able to run locally antique codebases that haven't been used in a long time. I was caught off guard because a simple install of an unrelated application with homebrew destroyed a big part of my work flow.

Macports never did this and kept libraries side by side cleanly.

Now, this is from the point of view of a software developer with a specific niche requirement. For normal users, from a security standpoint, it would most likely make sense to remove old versions of openssl.