For an interesting article on the adverse effects of a rule (as opposed to a discretion) excluding improperly obtained evidence, and the ways in which fact-finders can be biased by knowledge of excluded evidence or by suspicion that evidence has been excluded, see Tonja Jacobi, "The Law and Economics of the Exclusionary Rule", available at http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1783863
The author cites studies that suggest juries do not obey judicial directions, and even go to the extent of counter-intuitively reasoning that "if I am innocent I may as well commit offences because if tried I would be likely to be convicted even if innocent." We need to know how valid are the studies that are cited in this paper.
