OK. Simple solution: Start speaking out!
I don't see how this Muslim is doing that. He doesn't need to talk to non-Muslims; he needs to talk to his fellow Muslims and convince them to unite and eliminate this cancer from their religion; because if they don't, then the rest of the world is going to indiscriminately impose the solution from outside, and then there will be no such thing as Islam.
So this guy's little public relations "crusade", while well-intentioned, utterly fails to focus the persuasion and anger where it is most needed: on those who have ostensibly hijacked his religion: those are the people who need to be destroyed.
If there were Christians running around blowing themselves up and slaughtering civilians indiscriminately, we would take care of business and wipe such fools out.
Why can't Islam clean it's own house?
You are correct. Germany was a Christian nation in WWII. They were a violent nation that wished us harm, destruction and obedience to them as the overlord. We killed them until they unconditionally surrendered and most importantly disavowed themselves from belligerence. You can defeat your enemy on the battlefield but until his will to harm you is ended, you are not finished. Sometimes this takes a lot of killing.
General Sherman devastated the South on the battlefield and city and states and civilians that were an integral part of the war effort. Civilians may not be the soldier carrying the gun on the battlefield. They make the guns and grow the food for the soldier on the battlefield. What Sherman did was brutal and obscene. War is brutal and obscene. It worked, and he was just doing his job. It is really that simply.
If you are not willing to kill your enemy and all that stand with him, surrender for he has already defeated you. War should be avoided if at all possible. If you go to war it must be violent, brutal and deadly to all that oppose you be they soldier or civilian. It is an ugly obscene business. Avoid war if possible but if not, "Cry Havoc and let slip the dogs of war." It is ugly.