Sorry to say it, but you simply cannot have an honest, rational debate with insecure people.
You try to argue facts, they just deny them or bring out the insults (and it's orders-of-magnitude worse if different races are involved). And they will never admit that they're wrong.
It's certainly got to be one of the most frustrating things in this life - ESPECIALLY when you know an honest debate is needed.
Do you think there is anything to debate about? Just speak the truth and watch the sparks fly?