Sorry, but the reported inclusion of Spider-Man in "Captain America: Civil War" is, in the long run, a huge mistake for the Marvel Cinematic Universe.
First, it diminishes Captain America! The name of the film is "Captain America: Civil War", NOT "Avengers: Civil War". Chris Evans' Captain America has seen an upward trajectory in popularity with the masses from his first film, through "Avengers" to the surprisingly robust box-office for "Captain America: Winter Soldier".
In the past six months, Cap's third solo outing has morphed from what looked to be an interesting and exciting showdown with his friend Bucky to having to basically share top-billing with Robert Downey, Jr.'s Iron Man in his own film to now also sharing screen time with ScarJo's Black Widow, Cap-centric character Falcon..NOW you want to add Spider-Man?
Second, the people who think adding Spidey to this already overstuffed film - aren't these the same people who complain films like "Spider-man 3" failed because they have too many characters? Seriously, how is SOMEONE not going to get short shrift here? Captain America risks being an afterthought in his own movie. After moving to have a greater role in "Captain America: Civil War", even Robery Downey, Jr.'s Iron Man, one of the two main antagonists, risks having his role diminished as well.
What about Bucky Barnes? Or the Falcon? Or a certain other character..
Third, Marvel risks making Chadwick Boseman's Black Panther less important - which would give less of a bounce to his upcoming solo film. Seriously, it was Chadwick Boseman who electrified fans by walking in between Chris Evans and Robert Downey, Jr. four short months ago. He was supposedly going to fill the Spider-man role. Now that Spider-Man is available, Marvel risks making the character far less important, which can only hurt him in future films.
Fourth, Kevin Feige has explained that superhero do not exist in the Marvel Cinematic Universe, what is the point of having Spider-Man in the film in the first place? The film will be more about world governments demanding accountability and oversight of superheroes instead of them forcibly revealing their true identity to the authorities.
So, without the "big unmasking" from the comics, what is the purpose of having Spider-Man in this film again? Without his friendship with Stark? Without anyone in the MCU knowing who he is?
This has the potential to be a humongous mistake.