It has an upside and a downside, both significant. On the upside, it allows people to dedicate themselves to it with the attention of a vocation. On the downside, as a career it becomes their entire livelihood, and that creates an incentive to benefit themselves at the expense of their constituents, the electorate as a whole, and the international community. Actually, the dilemma is much the same as with other professionallizations of previously volunteer services such as police and the current arguments over privatized fire services.
In the balance, I prefer politicians to be as non-career as possible, but recognize that the complexities of statecraft put some practical limits on how well a non-pro can do the job. Of course ideally the professional aspects could be handled by competent and fairly paid civil servants and advisors while the decisions are made by elected volunteers barred from themselves associating with lobbyists.
