While Stan Marsh is a smart kid, I don't see that this is an earth-shattering or valuable insight. It's just the same old cop-out from politically uninterested people.
While the major party candidates may have problems, there is no way for either of them completely acceptable to a large number of people. The Republican and Democratic nominees head up huge constuency coalitions (that's what those parties are) and thus have to compromise, from the perspective of almost any individual, on a great many issues.
I was watching O'Reilly last night, and he had on social scientist of some sort discussing why so many people don't vote. This guest was explaining that while people like O'Reilly grew up in an environment where understanding politics and government policy, and voting, was encouraged, many people don't. Thus they lack what she called a "wide political spectrum" in their thought processes. It wouldn't occur to them how important voting is. Of course O'Reilly, disdaining nuance and subtlety as usual, said that non-voters are just lazy, and if they think the choice is between the "lesser of two evils," they should make the choice anyway and vote. It's their duty as citizens.
It's not often I agree with O'R over Stan Marsh, but this is one case.