in legends the two got a bit muddled, since the temple guardians were said to study the deeper mysteries of the force, including the dark side, and thus usually wound up grey jedi.
one of the things Canon dropped thankfully, though given that we have a canon Temple Guardian turned High Inquisitor in Rebels, the idea that the guardians sometimes studied things in the archives that they shouldn't have certainly would seem to apply. though honestly i'm surprised that at how few jedi actually fell to the dark side during the clone wars.. on screen at least. Fighting a war is about as antithetical to the jedi philosophy as you can get. part of the reason why the question of "how does a true jedi fight a war" was such a recurring theme in the later seasons of Rebels i think.
I think there is some confusion here.
I'm referring to Sentinels in the 3 "class/role" paradigm of the Jedi roles.
As I understand it, Sentinels, were between Guardians (Warriors/LS Duelists) and Consulars (Healers/Diplomats/Superior Force Sensitives)
It came down to how they used (preferred/favored) the force. Through their Body or through their Mind essentially.
Sentinels favored both paths equally & also favored mundane skills (Blaster usage, Computers, Lock Picking), and were often attached to the Civilian Government in roles like Law Enforcement or Ship Piloting etc etc.
I think these roles originally came from a Video Game but have made there way into canon.
Temple Guards could be Sentinels, but not all Sentinels were Temple Guards.
They were still very much Light Side force users.
As for a War..... Well it helps that the Clone Wars enemy was a heavy droid user. So that wasn't "killing".
The Jedi philosophy is to kill only as the very very last resort (after many many attempts at subduing w/o a death strike).
Maiming someone w/ a LS to the leg or arm on the other had seems to be a perfectly acceptable response to violence. :)
There seem to have been quite a few either during the Clone Wars or directly after in both canon & the EU that fell to the DS.
We just don't get a lot of detail about most of them.
The Inquisitors obviously had some.
Dooku & Pong-Krell were a couple.
I recall in I think the W-Wing series or I-Jedi there was a story of 3 Dark Jedi fighting the ancestors of some of the book's Pilots, along w/ possibly Obi-Wan from the description. In the years just after Order-66 when they were being hunted.