The courts are inherently adversarial. In criminal court, you have the State/City/Federal Govt. and you have the defendant. The whole idea is that both sides have effective legal representation and a competent jury to determine the facts of the case and as a result, justice comes out of the process. Civil court is similar, except that it’s not the State vs. a defendant, it’s a plaintiff who is claiming that someone else (the defendant) did something that caused them damage of some sort- they broke a contract, they destroyed/damaged something, they didn’t hold up their end of a bargain, and so on. Again, the whole idea is that both sides have effective legal representation and a competent jury and justice comes out of the process. The whole point is that the defense does their damnedest to convict, and the defense does their damnedest to get their guy off the hook, and the truth comes out, and the verdict and sentence reflect that.
Justice isn’t necessarily done when someone has ineffective counsel, or the system works against them, or things along those lines. But the adversarial nature is inherent to the idea of a court system.
I suppose what you’re talking about having are called “bench trials”, where a defendant is tried by a judge, rather than a jury. These exist, but in the United States they’re at the discretion of the defendant (jury trials are constitutionally guaranteed) - if they feel like they’re going to get hammered flat by a jury, they may choose to have the judge try them and decide their sentence, as sometimes a judge is likely to be somewhat more lenient than an angry jury might be- they know the law, they’re more likely to be dispassionate, etc… Which may be bad in some situations, but in others it may be a whole lot better.
As for the governmental aspects, what you’re describing is a direct outgrowth of what @Northern_Piper points out- the rise of “factions” as the Founding Fathers called them. They’re also called political parties. And it doesn’t really matter whether it’s a first-past-the-post system like the US or UK, or whether it’s a more parliamentary coalition model like Germany or France, the whole shebang is centered around the idea that a party will stand up for its constituents, be that by allying with other like(ish) minded parties, or by opposing other parties. It’s just more… intense(?) in the US and UK, because with two parties, one side is in power, and the other side is not, and rarely does either have a dominant position. So there’s a lot of political hay to be made by opposing the party in power. In systems where governments are formed through the building of coalitions, the “other side” is less starkly defined- your party may or may not be part of the governing coalition or not, depending on where it positions itself and allies itself. But again, the whole idea that you’re sticking up for your constituents means that being part of the opposition is necessary.
The other thing the OP is missing, is that we’re talking about the sausage making. The bureaucracy that actually runs stuff and is ordered around by the political types is much more top-down than the political side of things. There’s a politically appointed head to say… the Department of Transportation, but below him there is almost certainly a level of civil service management who do their jobs regardless of who’s in power, and whose underlings are the same way. That stuff is NOT politically adversarial, at least not typically. We did see some under Trump with the insertion of political demands into what are essentially scientific statements with the NOAA/NWS w.r.t climate change, and to some degree with the USPS and DeJoy’s shenanigans with sorting machines, etc… But that sort of thing is most emphatically NOT typical of the way it’s done in the US.
“Many forms of Government have been tried, and will be tried in this world of sin and woe. No one pretends that democracy is perfect or all-wise. Indeed it has been said that democracy is the worst form of Government except for all those other forms that have been tried from time to time.” - Winston Churchill
Consider what a non-adversarial government would look like. The world has provided us with plenty of examples. The regime in power presents the official viewpoint of how things are and everyone else must agree with that viewpoint. There is no basis for assuming that this one allowed viewpoint is the best one, or even a correct one.
An adversarial system allows multiple viewpoints to exist and allows them to engage in conflict with each other. It is more likely (although not guaranteed) that the viewpoints that emerge from these conflicts will be better ones. Good ideas are generally stronger than bad ideas and true ideas are generally stronger than false ideas. So in an arena where ideas are allowed to compete, the good and true ideas emerge as the winners in the long run.
The military has war games for this reason. You have red teams that are literally the opposition, and you (fake) fight it out. Industry regularly will give multiple teams different goals and have them compete internally to see which path to take.
In the short term, adversarial processes often look very wasteful and messy, but in the long term they let you fight things out at relatively low stakes and adapt. Organizations that attempt to completely eliminate opposition become fragile command-control shells because they don’t adapt to any adversity. Eventually the reality of the situation comes crashing down and the whole thing collapses.
Parties are a stable equilibrium given some legislative rulesets. A group of unaffiliated legislators who simply votes individually and never bands together will get a lot less done than a bloc that unites behind a shared plan and agrees to support each other even when they don’t 100% agree on every part of that plan. Can’t represent your constituents if you don’t get bills passed.
Yes, yes, yes, I asked, was answered, and as I said before, seven posts upthread, “Thanks for all the responses and this has been really interesting food for thought, especially bringing to light things that I obviously didn’t consider.”