******
Just because you both enforce the law, does not mean you are associating with evil. The law isn't evil, and if you aren't helping him, then neither are you. That'd be similar to saying, well, that fire giant over there favors swords, so from now on I will only use maces, because I don't want to be even remotely associated with evil.
*********

First, let's look at the defenition of "Associate"

as·so·ci·ate Audio pronunciation of "associate" ( P ) Pronunciation Key (-ssh-t, -s-)
v. as·so·ci·at·ed, as·so·ci·at·ing, as·so·ci·ates
v. tr.

1. To join as a partner, ally, or friend.
2. To connect or join together; combine.

Or.....
To join in or form a league, union, or association


Now, in your first example, of both being Tribunals, I think you are completely wrong. yes, the Spire itself is not evil. Yes, the law itself is not evil. But it has an evil god, and an evil provost, and evil magistrates....so...to JOIN that ASSOCIATION, is, at least in my view ASSOCIATING with those evils who are members of that association. It doesn't matter if you don't like them, or don't help them...you are ASSOCIATED with them, by "joining together" with them.

Your second example, to say that consciously JOINING an ASSOCIATION that has evils in it, and is run by an evil god is morally (in cf terms) equivalent to using the same type of weapon as some evil ...is a specious argument at best.