Firstly, I apologize for the insane length of this comment. Note that I also have not read the comics so I'm analyzing purely based on what was seen in the films.
In regards to the discussion between Christian and Tom about Cap's motivations and the Accords:
To go with the cop metaphor, Cap's concern is more specifically that the Mayor's Office (U.N.) will tell the cops to answer this 911 call which may be nothing more than "my neighbor's dog keeps pooping on my lawn" while telling them to ignore the 911 call saying "Help someone is robbing my convenience store", and/or that the Mayor's office will only reach a decision three days after the 911 call was originally made.
To also coincide with Christian's television observation, if you look at all the films with Cap, you can see a coherent story arc that leads to this perspective (even if some of it may be retrospective projection).
First Avenger: Steve has a clear enemy to fight with a morality informed by the time he grew up and challenges America faced.
Avengers: Steve is a man out of time that is struggling to make sense of the world, only to finally find himself once again during the Battle of New York.
Winter Soldier: Steve butts heads with SHIELD, a secretive organization bogged down with politics, bureacracy, and questionable ethics that suggest that their targets may be chosen based on personal interest rather than greater good. Oh, and it's actually Hydra.
Age of Ultron: With SHIELD largely dissolved, the Avengers are left to try and clean up Hydra themselves. In the process, Steve becomes leader of the Avengers, allowing them to remain autonomous and taking on targets the governments may not be able to.
Civil War: Steve fights to keep the Avengers from becoming another SHIELD.
They don't say it as much, but his character manages to remain consistent while growing from movie to movie. As such, we can contextualize his reasoning. The U.N. is designed to keep other governments in check, but Avengers are not a government. They are a specialized force, and Steve believes it is better to act on their own than to have governments bicker about whose interests matter more.
Any connection I make to Winter Soldier is my projection, but he clearly states that he doesn't trust being restricted to the U.N. where there will be agendas and prioritization of targets based off of questionable motivations.
However, it also clearly becomes apparent that no matter the pragmatic causes for the division, in truth the conflicts are all personal. Which perhaps makes it a wonderful allegory for modern political discourse.
As for Black Widow, I think this film has her internal conflict of trying to figure out the right side to fight on. We discover in Avengers that she used to fight for the "wrong team", and in Winter Soldier all this time she thought she was working for the good guys when it turned out to be the bad. Now she's struggling to figure out which side is the right side, and why her turn at the airport works for me.
I'd also love a Scarlet Witch solo film. Following Civil War, we have ample room for her to do something like go on sabbatical in an effort to figure herself out, have an adventure, and through that conflict find a resolution as to who she is and what her goals are. Don't think we can anticipate one in time for Infinity War, sadly.
As for the 3x3, I'm gonna side with Kelly that smackin' the tire is not exercise but training. The context in which it is presented in the film suggests that Bruce Wayne is preparing for his showdown with Superman rather than simply being a regular part of his regimen. Bruce Wayne waking up and immediately doing push-ups in Batman Begins is an example of a regular exercise regimen rather than being part of a training montage (and also pays off with a "what's the point of all them push-ups if you can't even lift a bloody log" gag later).
What I wish I had included is actually Don Juan, where Joseph Gordon-Levitt's character is constantly working out each day by himself until the end, where instead of this solo activity he decides to play basketball with the folks that are always at the gym. A significant indicator that he is breaking his old habits and is changing as a person. Can't believe I forgot about it.