1) Verita serum is difficult to make (this is noted several times), so not something to throw around everywhere.
2) Laws regarding individual rights. Consider this: if the U.S. (or UK, or whoever) started administering sodium pentathol (sp?) in every case of criminal accusation, the ACLU and other lawyers would be…

Veritaserum for one, requires at least a month of preparation. Veritaserum also only forces the user to admit what they perceive to be true. Thus, if someone had been confounded or put under a memory charm, they would only state that truth.

For instance, *SPOILERS*


Bertha Jorkins, if she had been given Veritaserum and…

Yes - there is worldbuilding behind the scenes of any fictional story that takes place in anywhere other than the here and now, and then there is the kind of world-building that is the central part of a story/book/series. Harrison is dismissive of the 2nd kind.

The only solution to bad worldbuilding is better storytelling. M. John Harrison said it best: