As noted by Travel.ru, the issue of the legality of this ban may now be brought up for discussion in the relevant committee of the European Parliament.
Ryanair explains its actions by saying that it does not have the ability to check the visas of citizens of other countries during online check-in, and therefore requires them to check in at the airport. If the airline brings a passenger who does not have the right to enter the destination country, it will have to pay a fine of several thousand euros and take him back at its own expense.
The problem, however, is that check-in at the airport with Ryanair is paid – £4 or €5. Thus, non-EU citizens have no way to avoid paying this fee, even if they are flying without luggage and want to check in online. True, Ryanair offers them to get this money back later through a claims process, but few people actually use this lengthy method.