Mark's wrong. [Correction: Mark is right on the larger point, but wrong on the small Herring bone I'm going to pick.] In Herring, cop checks Herring's record in two counties for outstanding warrants, after Herring had arrived at the county sheriff's department to retrieve something from his impounded truck. Neighboring county (erroneously) confirms there is an active arrest warrant out on Herring. Cop arrests, searches Herring's vehicle incident to arrest, finds drugs and gun.
Cops can do as many warrant checks as they want, on anyone they want, for any reason or no reason at all. So the problem here isn't "personal animus" (even if there was personal animus). The simple reason Roberts et al. get it wrong is that, quite obviously, there is every "reason to believe that application of the exclusionary rule here would deter the occurrence of any future mistakes." How long do you think it would take the neighboring county to get its act together after this f***-up led to a reversal of a criminal conviction? Not very. Easy questions like this aren't supposed to make bad law.
