The Wardens are of particular interest to me, after some extended study of criminal justice programs. Dresden uses cop analogies for them, but that doesn't really apply.
They're Special Forces. They're not investigating a crime, or bringing in someone for questioning, or even bringing in someone for a trial. They're getting to a high-priority target. If they can reasonably take that person down without undue risk to themselves, great. If not, lethal measures are necessary. You're dealing with warlocks, those who have enough power and a willingness to disregard the Laws. They can summon demons, kill with a ritual, or invade someone's mind if they're not prepared for it. They're dangerous threats that need to be neutralized.
The ones that get a trial are usually just for show, but that's because they always backslide. When a warlock backslides, people die. The two trials that we see include the Merlin personally soulgazing one (who was also obviously insane), and a full confession from another. Even Harry, who has huge reservations about the Wardens, recognizes that there really is only one way to deal with true warlocks. He argues for prevention, not clemency.
Anyway, that's what I think about it.