Corporate politics don't make you steal from your company. "Sidelined" wouldn't be a defense for direct embezzlement of funds, and it's not a defense here.

If he felt the way you describe, he should have gone off and started his own thing (he did!) maybe sold it for lots to someone else (he did!) and not steal tech from his former employer (fail!)

We all get fed up with work politics, not having our opinions prevail, etc. We don't all walk out the door with countless hours and millions of dollars of work product.