I think there needs to be a sense of perspective over this issue.
In many respects Ryanair is no different to any other airline. They all want Commanders to take minimum legal fuel whenever possible and subject to weather and route etc this is a perfectly reasonable request.
The issue is whether their Commanders feel they are subject to any undue pressure when electing to carry more fuel than legally required.
In law of course only the Commander has the absolute right to decide on the fuel required for a flight.
With respect to mechanical malfunctions, once again these can happen to any airline - given the large number of movements which Ryanair conduct on a daily basis, you wouldn't be surprised at a few landings enroute etc due to a technical problem.