Had he been faithfully doing good Warden duty until then? Or was he dragooned into service as a Warden because of the Kemmler situation? ...
You know... I think we
don't actually know very much about Justin's past.
Maybe he
was dragooned into the Wardens to fight Kemmler, just as Harry was dragooned to fight Kemmler's heirs... That's not my impression, but I don't recall any canon I can quote, or WoJ I can link, to show support for the "long-term warden" as Justin's backstory.
...
Taking Bob1 doesn't violate a single Law of Magic. Bob isn't black magic. He's knowledge not quite incarnate. Naked power. The good or evil of Bob is almost entirely in the holder ...
Not so.
Recall that when Harry re-united Bob with Kemmler-era Bob, we got Evil Bob.
Evil Bob is... well,
evil. Just having the memories made the change -- Harry was still the Boss of Bob, technically (even EvilBob had to obey the return-to-skull conditions Harry had laid down), but Bob tried to
KILL Harry; and you recall the WWII-Nazi bit of the Nevernever that EvilBob cooked up.
If Bob were as neutral as all that, destroying the skull wouldn't have been a priority -- Bob could have "safely" been retained and studied by the Council. Instead, it needed to be destroyed... "of course."
Early on in the series, Harry explains (or sometimes just narrates what/why he can't explain) to Murphy how some research will get him killed, if the WC were to find out. Some knowledge is inherently Black-Magical, or at least a presumptive death-sentence.