Laws aren't being contrived. The laws, case laws specifically, that speak to the reasonable standard are well established. It is rare that any new cases come about that affect the courts interpretation of reasonable as the standards have been heavily analyzed. The exercise now is how to apply these standards to the facts of new cases.

What you should have said, Hank, is that agencies need to more closely scrutinize what is an arrestable offense. This is a matter of policy again, not law.

Generally what is an arrestable offense should take into consideration the governments (state, fed, or local) interest in apprehending the person and stopping whatever it is they were doing and the benefit to the public in doing so.

Selling single cigarettes doesn't seem to be a very compelling reason to take someone into custody. This call was made by the dept and the officers on scene cannot be faulted for that.

A good example of new circumstances directing how existing standards are applied is the use of tazers by law enforcement. Being a fairly new tool, the courts are still ironing out how to apply existing standards to the use of that tool. There have been some inconsistencies from district to district so far, much more so that in more well established force application tools. Time will iron those things out though. Hesterberg vs. the US is a good recent example and probably the most comprehensive discussion on the topic thus far.