I've read the thread, and if anyone mentioned that the so-called "taxes" are not returned if you cancel or do not turn up, I missed it.
So the policy of overbooking, which of course FR has, is usually quite lucrative.
The only one of the taxes which is not just another charge by Ryanair (or any carrier) for the service(s) provided is the Government tax. This is a small proportion of the total amount added to an apparently cheap fare as "taxes".
The remainder are the airport's charges to the airline, not the passenger, for its services, and various additional charges dreamed up by increasingly imaginative locos. (Charges for:- Making a booking, Making the payment for it, Checking Baggage, Putting fuel into the Aircraft ("Surcharge"), Breathing etc etc).
Of these, it is illegal not to return to a passenger the Government Tax that is collected with the ticket price, in the event of cancellation or "no show". This money does not belong to the airline which collects it. It belongs either to the Government or to the passenger , and refusing to repay it amounts to theft.