I think idiot's voting for your candidate is corrosive to that political party. Take republicans and farm subsidies they are directly in opposition to most of the "core" principles of personal accountability, free trade, less government etc but try and find a republican in Idaho that does not support them.
That's not a product of idiots voting. It's a product of compromise.
The US system, favours a binary choice. You vote A or B. Australia (where I live) is even more this way. It's a stable sort of a system. Governments are fairly powerful. There is less need for the shaky post election coalitions of different systems. But it comes at a cost: Compromise.
Republicans (from what we hear down here) get votes from social/moral conservatives, religious conservatives, social libertarians, nationalists, militarists, & lots of other subgroups. Then you get these smelted into traditional voter groups. So an rural area in some part of the US with a certain religious, moral, social & historic heritage might be generally sympathetic towards a militarist, nationalist, socially conservative & religious party. In the US of 2008, this is the Republicans.
Along comes a decade where the region stands to gain from certain policies. For technical reasons, these policies are at odds with the part of a political theory at the centre of their parties history. This is the part of the political theory that supports less government intervention in their lives, a lot of freedom over their property, personal lives, & a lot of other stuff that they like. But the link between economic policy & individual liberty is very academic. They just want the damned price of canola to stay put.
Under a different political system (say Italy's), this issue could cause a party split. Lets say, the ICP (Idaho Conservatives Party) is formed. They put a bit more emphasis on this & a bit less on that but stay close to the former party line. The difference is they support the subsidies which benefit their voters. They join the coalition that the Republicans now need to form government because three of four of these parties split. This allows the ICP to focus mostly on subsidies & a few other issues that are important to their electorate.
The ICP is free to say they mostly leave issues other then sex education, subsidies & genetic patenting to the Republicans. The Republicans are free to admit that they don't like subsidy A, but it's a small price to pay to form Government. Otherwise they would have to get a different party on board with different compromises or reform the government. Theoretically, this allows parties to stay loyal to core principals.
Deals get done either way. The US's system is more stable. But you could argue it's less Democratic. Minority opinions are under represented. Voters make bigger compromises & get a less granular control over what their vote means. This is probably felt more now that there are several divisive issues on the agenda.
Just FYI, there are (at least in the US) multiple meanings of "social libertarian". Most people I know that would use that label for themselves are closer to being a classical anarchist or socialist, and do not vote Republican.
