[patrickmay]

Many (most?) issues don't fit on a single dimension. Using your example, people hold positions that include "Absolutely!", "Yes, but also the rights of the mother.", "Yes, but I won't impose my beliefs on others.", "No, but I don't think people who feel otherwise should be forced to pay for abortions through taxes.", and many others.

In addition to the problem with biased questions you note, there are often built in assumptions that make yes or no responses impossible.

[Nathanba]

it's far worse than that, people don't even agree on the definition of words. In this example what a 'child' is.