Movie Scenario or plot

Rating: 1/10 (29 April 2019)

This movie is a screw up for all the movies.
This scenario of Time Machine changes the whole concept of the world or the Marvel Universe.
If the good guys or super heroes can multiple times change the past, then why can't the bad guys or villains.
Of course the heroes return back the item so that, they do not to change the time line.
Let's talk about what could happen if Thanos or some mad evil scientist do something far more evil deed in the universe with the use of Time Machine.
By chance kill Adam and Eve so that they kill all human existence.
Or
Something far greater Sevier he goes on to all planets or universe and kill the first born or species.
And so destroys the whole universe
Now let's get back to Marvel film.
Since we are talking about Time Machine. There will be all the time 2 people exactly the same, one from that period of time {(for marvel Endgame Movie) past} person and the (Future) person.
Captain America (future) goes back in the past and marries Peggy Carter and stays in the past also gets back his unbroken shield to Sam Wilson.
Doesn't this tamper with the past. Having an extra human being also with the actual Captain America Shield. If means the (past) Captain America doesn't have the Shield.
Also Nebula (future) kills the (past) Nebula. Doesn't this erase herself from existence. As without the past self, the future self cannot live on.
There was also a scene where Iron Man and Ant Man steals the Space Stone.
So a secured and lock briefcase opens with a drop to the ground, without any force. Also Loki disappeared with the Space Stone in 2012 which will also cause problem with the time vortex. As something happened that weren't suppose to happen.
Also the Avengers all get their stones without any hassle or fight. Something spicy should have been added.
What I mean is new villain or "Jarves" should have turned up the alarm for intruders. etc.