I don't have any problem with the principle of printing your own boarding card pass at home, or paying to have it done for you at the airport if you don't.
But if the latter, the charge should bear some relation to the actual cost, to Ryanair or the handling agent, of doing so - otherwise it's just a fine/penalty.
Yes, of course you are deemed to have agreed to the charge in your ticket contract/conditions of carriage, but contract terms still have to be fair and reasonable.
It would be fascinating to see this tested in a court of law.