What is the name of the survey question style that forces a choice between non-opposite pairs of items, and why is it used?
Short answer
Forced-choice task

Background
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  ...tests that force one to choose...


Such tests are generally referred to as forced-choice tests in psychophysics. There are many applications of these tests. In general, AFC tasks are less biased than for example yes/no tasks (Yushurun et al, 2008). A sample paper on an AFC test for personality testing is Christiansen et al. (2005).

References
- Christiansen et al. Human Performance (2005); 18(3): 267-307
-  yushurun et al. Vis Res (2008); 48(17): 1837-51