Because the law of the Pharisees was the law of the authorities in charge, their law is no different than Roman law or United States law. But I think that is different than the Law Christ was talking about when referring to the priests who are "guiltless". I believe Christ is using a higher law, a law at the level to which Pharisees raised their own law, as an example.
The Pharisees had begun to raise the importance of the Talmud/Oral law as equally authoritative as the Mosaic Law. So looking at the verse about the innocence of the priests.
Mat 12:5 "Or have you not read in the Law, that on the Sabbath the priests in the temple break the Sabbath and are innocent?
Again, the issue or focus is the sabbath. The Pharisees had added so many rules and restrictions to the Sabbath rest, that Jesus had to remind them that the priests had a responsibility to offer sacrifices on the Sabbath. Those sacrifices necessitated offering the regular daily offering plus an additional offering of two lambs. The preparation and actual activity surrounding the sacrifice was considered servile work by the Pharisees if I remember correctly and that's why Jesus said they were guiltless. There was preparation of the animals for sacrifice; i.e. slaughter, skinning, etc. They were not violating the Sabbath but performing the requirements of the law for the Levites and priests. That's how they were keeping the Lord's day holy.
That's why Jesus said the priests were not guilty...because the Pharisees were accusing Jesus of breaking the law at every possible opportunity, especially those of the Sabbath.
But when the Pharisees saw this, they said to Him, "Look, Your disciples do what is not lawful to do on a Sabbath."
In Matthew 5:1-8 the word Sabbath occurs 8 times (NASB) so it's obvious to me that the Pharisees were trying to accuse Jesus and Jesus was refuting their legalistic additions and misinterpretations of the Sabbath. I do not see Jesus advocating nor encouraging nor permitting violation of any law ever.
I always learn from these discussions and though sometimes we disagree, I respect the fact that study and different views serve a purpose and bring us a better understanding of the whole picture.
Thanks for making us dig deeper, Keith.