Portmaster is one of the first tools new users will encounter when coming to FreeBSD. The /usr/local/etc is very different than what they are likely used to. They are still likely to place a portmaster.rc file in /etc. It's completely disingenuous to suggest the user may put it into /usr/local/lib or $RANDOM_PLACE. There is absolutely 0 benefit to removing this check and >0 benefit to keeping it.