This is just my belief on it using the rules to define this:
For most arrests, they are on Non-combative jobs (Tech Expert, Janitor, etc) - as such they should be avoiding combat as much as possible, being arrested is not the same as being kidnapped and thus not something they should be shooting to get out of (There is other ways to get out of it from RP)
For the Combatives this would be even more stupid for them to do, as chances are your not being arrested for Murder but more likely Unprofessional Conduct, why would you ever do something to upgrade your charge from something minor to fucking murder (And in the rare case it is murder, RP that shit out, chances are you can get it down to Manslaughter)
TL;DR - This is an RP server first not a combat server, don't kill just because you got caught doing some stupid shit by ISD.