Why does the doctor put on the mask ??

It seemed to me he literally had been DRIVEN crazy by Michael not talking...

He had been treating Michael I think since Lomis died....and it seems his inability to get Michael to talk or communicate....Literally PUSHED him over the edge after so many years

He wanted answers, He wanted to hear Michael talk, He thought bringing Michael and Jamie Lee Curtis together would finally make him talk.

The reason he put on the mask was because he had just KILLED....for so long he treated michael, A serial Killer....well finally He Just KILLED.

He put on the mask and said "so this is what it feels like"

No one cared who he was until he put on the mask ...

He was trying to unleash his inner Busta Rhymes.

Because the film needed an unecessary plot twist in order to get Michael to Laurie, since he really has no motivation to personally hunt her down.

I thought that was dumb as hell but either way he got his

Because the writer's of this film are completely incompetent, wrote themselves into a corner and could think of no other way to force Michael into a confrontation with Laurie.

So they decided to have the doctor go crazy for no reason (and derail the whole film) and taxi Michael directly to Laurie's door. I honestly can't believe the level of terrible writing in this film. My jaw was on the floor at the sheer awfulness of this plot point.