Both sides are missing the point. The actual number of teams in the Premiership is a red herring, as is the issue of a ring-fenced Premiership. What both sides should be asking is how financially sustainable professional rugby is in England.
The current structure, with a fully professional Premiership and Championship - 24 clubs - obviously isn't sustainable. The likes of Coventry and London Welsh have proven that.
It strikes me that what is needed is a period of time where a clear distinction is made between professional and amateur rugby. Personally I'd guess (and it's no more than a guess, admittedly) that the game can support no more than 16 professional clubs in England.
Of course, it would be impossible to force an "amateur" club into not paying its players, but if the incentive of automatic promotion to the professional ranks was removed so would the chances of clubs bankrupting themselves in pursuit of the so-called holy grail.
It's not about ring-fencing the Premiership - it's all about ring-fencing the professional game.