Wanda Maximoff: Vision, are you not letting me leave?
Vision: It is a question of safety.
Wanda Maximoff: I can protect myself.
Vision: Not yours. Mr. Stark would like to avoid the possibility of another public incident. Until the Accords are a more secured foundation.
Wanda Maximoff: And what do you want?
Vision: For people to see you...as I do.
Clint Barton: The futurist is here gentlemen! He sees all. He knows what's best for you, whether you like it or not.
Steve Rogers: I know we're not perfect, but the safest hands are still our own.
Steve Rogers: This job... We try to save as many people as we can. Sometimes that doesn't mean everybody, but you don't give up.
Tony Stark: Captain? You seem a little defensive.
Steve Rogers: Well, it's been a long day.
Tony Stark: If we can't accept limitations, we're no better than the bad guys.
Steve Rogers: That's not the way I see it.
General Thaddeus 'Thunderbolt' Ross: Captain, while a great many people see you as a hero, there are some who prefer the word vigilante. You've operated with unlimited power and no supervision. That's something the world can no longer tolerate.
Tony Stark: All right, I've run out of patience. Underoos!
[Webbing flies in, stealing Captain America's shield and restraining his hands. Spider-Man lands on a vehicle, holding Cap's shield.]
Spider-Man: Hey, everyone.
Steve Rogers: I'm sorry, Tony. If I see a situation pointed south, I can't ignore it. Sometimes I wish I could.
Tony Stark: No, you don't. Sometimes I wanna punch you in your perfect teeth.
Scott Lang: I want to say I know you know a lot of super people, so thinks for thanking of me... Thanks for thinking of me.
Steve Rogers: Sorry, Tony. You know I wouldn't do this if I had any another choice. But he's my friend.
Tony Stark: So was I.
Chosen answer: We never get a specific explanation to what happens to him when he enlarges. Hank Pym explains to him that when he shrinks, it's the result of reducing the distance between atoms which is why he retains his original mass. However, being a giant with a mass and strength of only 160lbs would not be very advantageous in a fight, so they must have found a way for him to grow in size and strength in this situation. Ultimately, we just don't know - the movies and comics differ in a great many respects, so there's just not enough information to work with. Might technically qualify as a mistake, but it's something which could easy be solved with an in-universe answer, however scientifically dubious.
Phaneron ★