So many questions!
First of all, these are sheltered teenagers in a medieval society. Juliet is kinda shy and doesn't get out much. A masquerade ball is her only outing. When not sniffing flowers out in the meadow like Ferdinand the Bull, Romeo is hanging out with the boys.
I don't know what the families are fighting over, but Michael York's Tybalt and John McEnery's Mercutio are the two who are obviously undersexed and desperately needing a "release". We don't see Romeo's parents much but they seem too sweet-natured to be involved in any war fare. Juliet's parents have no issue with Romeo attending the ball and Romeo is only "bad" and outlawed after he killed Tybalt (if by accident). Also the friar and nurse are both happy about Romeo and Juliet together and both *think* the parents will eventually approve. Only nobody wants to be honest about the secret marriage ceremony and Tybalt's death throws everything out of wack.
Probably the biggest issue is that Paris is the "arranged" husband the parents favor. Juliet only "agrees" to marry him after she has a plan to get what she wants. Isn't this decision made after she talks to the friar with a solution: her fake death?
A bigger issue is the very slooooooow mail service by donkey and Leonard Whiting's Romeo sticking to what his teen friend tells him rather than waiting to hear the truth. Those impatient teenagers!!!! They are their own worst enemies. Had that letter explained everything, Romeo wouldn't have poisoned himself with so much gusto.
There was quite a bit of criticism at the time for cutting some key lines in the play because the cast was struggling a bit, being very young. Romeo + Juliet which was made almost three decades later with LeonardO (not not Leonard) didn't suffer in this way. However that cast was a few years older, mostly in their twenties and thirties. Not as old as Leslie Howard, but a trifle less believable than this version.
As far as instant attraction... who can explain that? I mean... juvenile Prince Philip squinted at Aurora in her crib in Disney's Sleeping Beauty but was all gaga when seeing her as a teenager "Briar Rose" frolicking bare-foot with hooty owl, birdies, squirrels and bunnies. Maybe Juliet was just a tyke when he last saw her. Or maybe he was blinded by Mercutio's obsession over him, constantly wanting to know where he is at all times as the jealous gay lover. I get him and Benvolio mixed up. Which dude kept saying it was too hot to keep fussing?
I didn't have a problem with them cutting certain lines and using more close-ups and short takes with the leads. But I do think Zefferelli condensed too much of the final acts so the whole thing is kind of off-balance. It's very slow and leisurely during the first hour and a half, then the last 38 minutes after the marriage, he has to hurry and get to the crypt scene. So it doesn't flow like it should.
I don't think Zefferelli is really using the lighting or camera angles to suggest any psychological complexities with the leads, which he should do. If Olivier or Welles had filmed it, we would have seen the darker aspects of this forbidden love. Instead Zefferelli relies heavily on the fresh-faced cast, the costumes and the soaring music.
I almost find Tybalt the most interesting character in this version. He's edgier and a lot more complex than everyone else. But after his death, there's a scene where the nurse is crying and says he was her best friend. Nothing earlier in the movie suggested they had any sort of real relationship.
I can buy Juliet being sheltered if she had an affliction-- like a speech impediment, a clubfoot or if she was agoraphobic. But this is a very wealthy family in a small city and they would have been riding in the streets to concerts and to church, and she would have been out of the house more and would at least have heard about Romeo who was her same age. Having them meet as strangers is just highly improbable.
As for marrying Paris, we know she's already wed to Romeo and cannot commit bigamy, and she comes up with a plan to avoid the second marriage. But we still need to see how she convinces her father she is now amenable to being Paris' wife. We go from a scene with her being defiant and the father screaming at her, to her suddenly having agreed. It's too much of a jump forward to be believable. She should really be agonizing about going behind her parents' backs and realizing she has to deceive her father. But we get none of that because Zefferelli is trying to rush to the crypt scene.
"You've had a few hours given back to you from life. A few hours in which to change your minds and your hearts. When you came into the grounds of this inn, you came into a place as it was a year ago today. You were in your own time, but the house and garden and Gwyneth and I are in the time of last year. The day the bomb hit. When you go away and walk up the road you will have spent a night in an inn. But if you look back from the crest of the hill, the halfway house will not be here...but if you remember, it will be as you remember a forgotten snatch of song. It will be a picture before your eyes. Gone before you realize it is there. Or an echo in the hidden places of your mind. But you have been here...and the world is what you make it." -- Mervyn Johns, THE HALFWAY HOUSE.