So you don't like UPnP – fair enough. I happen to find it useful for a bunch of dynamic stuff (mostly Mac clients -- BTMM etc.), but I also don't have untrusted clients on my network.
In any case, whatever your opinion about it may be, miniupnpd is included in the pfSense base install, and IMO it quite simply makes sense to perform this check, given how trivial this is to enable (port option).