Very much the reason why MacPorts requires sudo, so it can drop to a less-privileged "macports" user for builds, without putting your own user account at risk.
Not to rain on anyone's parade, but I find MacPorts to be superior to Homebrew in every way, from writing the ports themselves, to installing them and managing them. I used to use Homebrew some time ago, but when I got my Mac Mini, I decided to forgo it in favor of MacPorts and Pkgsrc (which Joyent also provides binaries of for OSX). Whatever MacPorts doesn't have (a rare occurrence), Pkgsrc tends to have it. If not, writing a MacPort is incredibly easy with their provided DSL.
I was pleasantly surprised that, despite Homebrew taking so much of the OSX package management mind-share these days, MacPorts still has an active and vibrant community going strong. I was also pleasantly surprised by just how well Pkgsrc works on OSX, despite its origins on NetBSD. In fact, Pkgsrc works so well that I've switched to using it on Slackware as my primary package manager for anything not in the base system, preferring it to SlackBuilds.org and sbotools (though I still use sbotools whenever Pkgsrc doesn't have a package I want — which sometimes leads to duplicate dependencies in different paths... still haven't figured out how to avoid that yet...).
