As the title states, why did Erik, the mutant terrorist known as Magneto, just leave his telepathy-blocking helmet at the end of Days of Future Past? A helmet he has personal attachment to, and had gone to great lengths to retrieve earlier in the movie. He just looks at it, and does his jesus floating off into the distance move.
No speculation please, direct word of god or interview answers only.
As acknowledgement of submission, and surrender.
Leaving the helmet is an indication that he no longer has anything to hide. If Xavier knows he can jump into Eric's mind at any point (and obviously Eric knows this), leaving the one thing that can stop such an invasion is tacitly indicating that he is effectively 'retiring', which we see confirmed in X-Men: Apocalypse.
He is making a statement that he no longer has anything to hide, and because he is not going to attempt any further 'misdemeanors', he won't be needing the helmet anymore.
Why did Erik leave his Helmet at the end of DOFP?
Was it really in his own hand at all?
He lost their fight, Professor X can control him anytime if he wants now and might never allow him to take it back either if he tried.
In X-Men: Apocalypse
We see him settled with his new family in peace. Until unfortunate things happen and then Apocalypse makes him a similar helmet to give him his freedom back.
The helmet is the only thing which can save him from Professor X's telepathic power, without it he is vulnerable.
