In my last column I argued that, whereas in dictatorships or quasi-democracies with inadequate constitutional checks and balances the loss of power can result in ruin and death for supporters of the losing party, in a healthy democracy losing is much more a matter of "that's the way the cookie crumbles – I'll beat you next time".  As a consequence, in a healthy democracy political parties do not exist to cling on to power at the expense of principle.  Rather, they exist as platforms for offering certain (albeit pragmatically- and realistically-determined) ideologies and policy programmes to the voters.  If the voters don't like our policies, they choose someone else – and no hard feelings.

However, this important advantage of a healthy democracy can be seriously undermined if politicians are professionals – if they do politics as a job, rather than as service or vocation.  If being a politician is your job, then although you may not die if you lose power, your career might.

Now of course it is true of any politician that she craves power – probably dysfunctionally more so than normal people do.  I think of political power-hunger as being a valuable form of dysfunction, much as football managers value greedy strikers.  Taking the responsibility of putting the ball into the net with thousands watching you and much depending upon it is a burden.  If your desire for glory offsets the unmanning effect of the pressure of the task, that's all to the good.  Similarly, being a politician involves often-awesome responsibility.  Politicians must choose that people should die, that people should lose their careers, that good people should have their property confiscated to subsidize bad people – and many other such challenging calls.  And if they get those calls wrong, disaster and shame beckon.  If the hunger for power prevents politicians from being unmanned by the magnitude of their tasks, then all to the good.

But although every politician should crave power, when your whole career depends on your obtaining power the equation is very different.  You no longer simply want power to wield it.  Now you want power because that is how you pay for your children to go through school, for that operation your mother needs, for that dream holiday you always promised your spouse.

Politicians that need power, rather than craving it, will be more tempted to compromise to get it.  Whereas the politician that craves power so that she can be the one that puts her ideas into practice will have limits to her willingness to compromise – for at some point compromise might make power not worth having – the same will be much less true of the politician that needs power to have a career.

If you lead a party of MPs that need power, they will care in a different way if they lose their seats or if the party is out of office for five years.  Those might be the key five years when an MP would be rising up the  front-bench ladder.  In government, such rises mean more money.  In opposition, they do not.

The consequence is that it is not enough for the leader to be independently wealthy, if her MPs are not.  And even independently wealthy people aspire to do something with their lives – for their lives to be meaningful.  If all that politicians have are their political careers, then even if they are rich they will be very strongly inclined to compromise to chase power.

If we want our MPs to lack principle and to be focused on day-to-day managerial issues – the drains, the housing problems, the other mundane constituency concerns – then one of the surest ways to deliver that is to make being a politician their sole job.  If we want our MPs to have principles and stick to them and to be our representatives in the Battle of Ideas, we should welcome them having other interests – not merely because they learn from them, but because they make holding on to power less important and holding on to principle more so.