While some of the killings that Mike ordered could be justified as "self defense" and strictly business, the reason I consider him an incipient psycho are the ones that weren't necessary.

Roth was a washed up ,broken down, ex big shot in FBI custody and would be hard pressed to cause any problems worse than the ones he'd already failed at.

The prostitute in the brothel was slaughtered horribly so Mike could put the screws to Geary. This was an innocent girl who was treated like garbage by Mike. She was murdered and presumably dumped in a landfill,lake or shallow grave. And for what?

Fredo didn't have to die. Mike could have given him a pass and exiled him from the Family.
Who but a true sociopath would kill his own brother.
Of course Mad Sam DeStefano killed his own brother,but that kind of makes my point.

Again,this is just my own opinion.