This isn't about making regulations and banning it, but the unions putting pressure on the airlines to make it more hassle than it's worth.
You cannot and should not regulate everything, but you don't need to make laws about everything (something our Government might want to realise) to ensure that things don't happen.
People have always paid for their own training. There has never been a time when commercial pilots only came from airline funded cadet schemes. Type ratings and line training are very different things than just getting a basic licence.