The point is that left-wingers tend to believe that all (or most) of the intelligent people vote left-wing, while right-wingers tend to believe that all (or most) morally upright (or Christian, or religious) people vote right-wing.
I tend to agree with you that, if ever such a restriction is passed and only high-IQ or high-morality people will vote, the outcome would probably quite surprise those who promoted either side; the high-IQ people will vote a lot more "right", and the high-morality people a lot more "left", than expected by promoters of such a limit.
Clearly not all high IQ people would vote left or right, but all the "high morality" people would indeed vote right. Why? because unlike inteligence or level of political/scientific/historical knowledge there is no way to measure or quantify morality.
Unless they simply wished to sow out the relatively small proportion of sociopaths all the high morality people would agree with whoever got to define what high morality was (is abortion a morally legitimate option for a potential mother? You said yes sorry not vote for you). The same cannot be said for high inteligence (given the following numbers 0, 3, 8, 15, 24 what is teh next number? it's not really clear that somebody who answers 35 is more likely to agree politically with the man who devised the question, than somebody who answers 76. the same applies to people who can correctly give the date for US entry into WW2, name the first US president or whatever other questions we might ask to test IQ or knowledge.)
But nevertheless this doesn't change the fact that promoters of "only high-IQ" voting, while accepting that high-IQ voters could think differently than them, are highly confident that they wouldn't do so; and similarly for pormotes of high-morality-only voting.
Since when is this a fact? As I said I think that restricting voting to the intelligent would be, well frankly just plain stupid, but that doesn't change the fact that there are certain political positions left and rigth that are also just idiotic. an intelligent and wellinformed person can believe in higher taxes or lower taxes, be for the EU or against the EU, for Iraq or against Iraq and so forth.
There are however relatively much fewer intelligent wellinformed and intelligent individuals, who would for example champion teching creationism in schoold to take a right wing example. On the left wing there resently was a great outcry in Denmark, when the the law that made it illegal for the banks to charge for the use of the national credit card, was changed so they could now charge 10 cent for each use.
The outcry continued untill the governement succumbded to the presure and made it so that the banks could only charge this money from the shops rather than the costumers, at which point everybody was happy. Cause it's not like if the shops would raise their prices to get the customers to pay anyways, right?
Such examples of gigantic cluelessness form the voting population just makes me sad (admitebly it's possible you could costruct a reasonable argument why letting the shops pay was better, but such arguments certainly weren't the reason for the measure).
(In any case, even if it were true that 100% of intelligent people were left-wing and 100% of moral people right-wing--which assumes there is no overlap between the groups, for starters--it would give us no guide at all for what the correct choice is in any specific situation; if the moral recommendation and the intelligent one clash, who wins? The nazis (yeah yeah, Godwin, whatever) were very intelligent, but their choices utterly immoral; on the other hand, one doesn't need to look hard to find groups of devoutly moral but naive and stupid people whose plans all come to grief due to lack of understanding of the world.)
That argument only makes sense if we assume that there is a negative correlation between inteligence and morality, if there isn't then it pretty much falls flat on it's face. IMO the reason why only letting some people vote is a really idiotic idea, is that it would lead to direct or indirect discrimination of the nonvoting public. It would also likely mean a high level of social unrest since it removes the options these people would have for expressing their dissatisfaction within the system.