The balance between like and dislike is probably because of their janus role. One the one hand they are force protection, including blue light taxis and patrolling the gut, and on the hand they are internal regulators.
The latter is where the angst lies and the waters muddied with barrier up/barrier down or aircraft guard both essentially force protection but with little threat. When the threat was finally recognised the barrier patrol was then transfered from RAFP to RAF and latterly (in many cases but not all) to dedicated FP. Counter Int, in the broad spectrum was also FP.
By mixing the two the opprobrium here appears to be aimed at the branch at a whole whereas it is the internal security side that is in the frame usually.
Did you know, not that long ago, that the Civpol relied on RAF expertise for IT forensic investigation?