If everything has a purpose then evil doesn't exist

[R-Farmer]

Textual legalism probably isn't a satisfactory response.

Unfortunately this is all anyone honest to the text can offer. That is if we are to speak where the text speaks and remain silent where the text is silent. That binds us to the context of this message. That being God does in fact have the ability and will to visit calamity upon whom ever he wishes, and here in Isa 47 he clearly wishes to do so to any nation of people who oppose his servant Cyrus.

This verse only applies to these people, that verse only applies to those - but, ofc, there's a verse for everything, and a whole chest full of convenient translations for each.  For every group of people past and present on a violent gods shitlist.  This is not..like discriminatory sentencing..... generally, behavior smiled upon by our courts - and so the context of judges and sentencing may make it even worse.

While this is true in many OT cases, you don't see this pattern repeating in the NT, or even today, which means there are indeed book ends or a time where this sort of thing happened which is no longer the case.

If I were to hazard a guess as to why it goes back to preserving his people and keeping His holy land sacred. When the curtain in the temple tore at the crucifixion all of that ended.
but me guessing is not the same as the Bible saying it.

God as described is a violent criminal, or a crooked judge Are you asking whether working with a violent criminal or crooked judge makes you culpable, or an accomplice? 

Do you know the difference between a violent criminal/crooked judge in this case, is the same between a terrorist and a revolutionary like George Washington, Jefferson Franklin Adams or any of the other founding Fathers. In that the winners of a conflict get to frame out and write history, those who have the most might, make the judgements on what is right.

Like it or not this is how all of human history works. So one man's crooked judge/violent criminal is another man's God.

I enjoy that you're comfortable with the notion that the existence of a god is at least fundamentally knowable - and that maybe sometimes it does fucked up things.  I do wonder if you'll be able to maintain a commitment to that position, and what you think it could possibly accomplish?

I can admit that people who oppose God for not complying with modern morality will see and think he's f-ed up. And alot of that perception come from their understand that God need be perfect or at least their version of perfect, which is based on their own version of morality. Not realizing that God can in fact rain down calamity/evil if He so chooses and still remain with in the parameters of what makes Him/them God.

I also think that it would be so much more useful if you focused more on why we should worship or serve a particular god (or anything, really).

 Your not gonna to like this answer but anything I say here will not be a valid reason for you because God does not align Himself with your 
Modern sensibilities or morality. 

So basically every argument I can make will always boil down to this: He is our final judge/He has the most might, Making whatever he says 'Right.'
Now, that said, you have been given the freedom to take this or leave this. We have also been given this life time to make this call. While I know this probably is offensive to many people especially those who believe in free will and that we are all unique and precious individuals. Which to a degree is the case.

 However More to the point Bible teaches we are all born slaves to sin. Sin, who's master is satan. Meaning we unless we elect to be redeemed and serve God. Our base instinct is to side with our default master Sin/Satan. Which is why we see what god does is wrong, because modern morality is at odds with god as most 'modern people' have not elected to be redeemed.
Which is apart of the reason why yielding to God's might/right is so offensive.

 I feel like discussions about how god did this or that or our lives are so and so can only be circumstantial.  So god did this, so god did that, so we find ourselves with a choice.  Okay...and?

I'm not really in a position (answering the questions you guys ask) to steer the topic without falling into the 'preaching' category.
If you want to discuss a specific aspect of salvation or in this case why we should follow god after the things he has done then you need to direct the topic by asking those types of questions.