The Speaker of the House of Representatives (Australia) is currently Bronwyn Bishop and there was, the other day, some issues raised over her bias. This led me to pose the question - why is the Speaker an MP? Surely they're going to have some bias if they're from a major party (which is normally the case) and it sort of defeats the concept of having an odd-number of seats. (I refer you to the House of Assembly in South Australia where there are 47 seats. The Liberals currently have 22, Labor 23 + 1 independent, and one undecided independent. If the undecided independent goes Liberal, it will be 23 each, making a hung parliament). Why not have a completely individual person (ie an official Judge) in the position of Speaker? Wouldn't that completely avoid the prospect of a hung parliament?
Firstly, it's not always the case that we have an odd number of MPs - while in some states/territories the number of MPs is fixed by legislation, in the Commonwealth House of Representatives, the number of MPs depends on the distribution of the population - at present, it's 150, which is of course an even number. (source) Thus, appointing an outside Speaker wouldn't always solve the hung parliament problem.
(In the rest of this response, I am going to refer primarily to the Commonwealth situation, but most of my points apply in some fashion to the States and Territories.)
To your main question now: each House of Parliament, for better or worse, has inherited the traditional power of the British Houses of Parliament to govern internal matters without external interference. (e.g. Commonwealth Constitution, s 49)
Among other things:
- Anything said in the House cannot be questioned outside of the House - there is complete freedom of speech inside Parliament. A judicial court can't punish anything said in Parliament - only the House can impose punishment.
- Each House has the power to punish contempts against the House, with the trial conducted by the House, and penalties of fines or imprisonment imposed by the House. (e.g. Parliamentary Privileges Act 1987 (Cth), s 7)
- It is a generally accepted practice that, while a House can compel a person to attend before the House as a witness, it cannot compel a member of the other House - it has to ask that House for permission. (source)
- The Commonwealth Constitution provides that election disputes are to be resolved by the relevant House. (Commonwealth Constitution, s 47) (This has been superseded by the provisions of the Commonwealth Electoral Act, which allows the High Court to fulfil this role - but if Parliament wanted to return to determining disputes itself, it could.)
(This list can go on and on - refer to House of Representatives Practice and Odgers' Australian Senate Practice for more.)
To bring this back to the role of the Speaker: as can be seen, there's a very strong tradition of parliamentary independence when it comes to determining internal parliamentary matters. Historically, this independence has been come at a cost - the Speaker of the House of Commons was historically involved in many disputes between Parliament and the King, and a number of Speakers were executed as a result. (source)
There has always been a strong notion that the Speaker is a servant of the House - the House, as a corporate body, can't actually execute its orders and resolutions, and relies on its servants to do so. One can argue that in order to fulfil this role effectively, the Speaker must be accountable to the House, and must hold the confidence of the House.
To appoint a Speaker from either the executive or judicial branches would risk compromising the ability of the House to fulfil its responsibilities. (Obviously, in the case of the lower houses, the Speaker is essentially appointed by the executive branch, from MPs who could otherwise be Ministers, but we'll ignore that for now...)
To quote William Lenthall, Speaker of the House of Commons in 1642, in response to a request from King Charles I while attempting to arrest some MPs:
May it please your majesty, I have neither eyes to see nor tongue to speak in this place but as this house is pleased to direct me whose servant I am here; and humbly beg your majesty's pardon that I cannot give any other answer than this is to what your majesty is pleased to demand of me.
Finally, while it has been traditional in Australia for the Speaker to come from the Government, that's not the case in all Westminster systems - most notably, the Speaker of the UK House of Commons is generally an independent. It's not completely unknown in Australia - for example, the NSW Legislative Assembly had the (now disgraced) independent MP Richard Torbay from 2007-2011. (Federally, we've also had Peter Slipper in 2011-2012, but his situation was rather unique - it was an attempt at adjusting the numerical balance in the favour of the minority government.) In the ACT Legislative Assembly, where Labor governs in coalition with the Greens, and the Government controls 9 seats out of 17, the Speaker, Vicki Dunne, is actually a member of the Opposition.
I don't think the system we have is the only system which can work - the current system has many flaws, and I'm sure if we tried we could come up with a system where an independent presiding officer could govern the House with as much legitimacy as the current Speaker and without breaching the separation of powers. However, we could do a lot worse than what we have.