St. Maximilian Kolbe may have volunteered to die, in order that another should live, but the reason why he was in a consentration camp in the first place was precisely because of his Catholic faith. He "lived Jesus" by "laying down his life for his friends," therefore displaying the "greater love" Our Lord spoke of in John 15.
I know, I know, I know. I'm not disputing the fact that Maximilian Kolbe is a saint and is in Heaven. He performed the ultimate act of charity. He died practicing the Faith but he didn't die for the faith. There's a difference.