"I'm not sure of your question, but I think you're asking how anyone can impede another's salvation if God has chosen His elect from before the foundation of the world. Is that it?"
That is it.
I support a missionary to Poland who is a printer by trade. He has had trouble learning the language and works as a printer there. Yet he has been a tremendous witness by his trade and love for the Lord and the people he has been called to. He uses the "Four Spiritual Laws" and anything else he can get his hands on to witness and it is effective. People are being saved one at a time and involved in his Bible study. Yet if you were to listen to his testimony, he always asks for a decision to trust Christ for salvation and people respond to that invitation. For Bunker to say he is creating "children that are TWICE the children of hell than they themselves are", to me is the heighth of presumption.
Bunker can be quite acerbic. I think there's a place for his kind of witnessing.
If God determines to open someone's eyes and ears, those eyes and ears will be opened by whatever means God chooses. I just happen to think a reformed approach is more pleasing to God as it more approximates the truth.
Most people require milk before meat. I did. But ultimately, meat satisfies more than milk. And those to whom He gives teeth, let them chew. 8~)