In all my 5 years with Ryanair I never had any excess fuel questioned so long as you stated the reason on the Voyage Report (and believe me if I thought extra was necessary then I took it!).
The issue seems to revolve around their Captains who have only ever flown for Ryanair from the cradle in combination with (a few) overzealous Base Captains putting them under pressure.
I gather the Base Captains are paid extra based on either on time performance or "fuel performance" (ie for the base aircraft/crews) and the BCs can opt for whichever they prefer.
This fact might explain why certain BCs put Captains under pressure to carry PLOG fuel. One has, of course, to question whether this method of paying BCs extra is really in the interests of flight safety.
If I was put under pressure in this way I would be inclined to file an SAIR (aka MOR) and also keep personal records (and details of witnesses) to be used in the event of employment issues.