there's a number of issues involved in the whole secondary ticket scenerio.
Firstly the club needs to make money and viagogo obviously pay them a decent wedge for their services, as for the seats in the third tier that they obviously give them for each match, this is unfortunate and I would much rather see these on open sale via the club but lets face it they rip us off in plenty of other ways (see price of nike strips, price of blue membership etc etc).
Secondly as many have put on here, you are not forced to use them, they dont pop a gun to your head do they. There's plenty of tickets going around on here so for users of bluemoon have nothing to worry about, just stay away from it.
Thirdly, this is my main gripe about the service and its not about the club nor viagogo but the city fans who hugely inflate the prices of the tickets they list. If they didnt do this the prices wouldnt be half as big a rip off as they are. Come on 'face value only' people then we could just moan about viagogo's over inflated fees!