Ken Hamm is essentially saying that if you don't believe all of it, why should you believe any of it? I don't agree with Hamm on much but I do agree with him about that.
Not just Hamm but so many fundamentalist christians understand the dilemma is an all or nothing proposition. If the Genesis story is undermined in any way, this throws doubt on the entire fall of man story and thus the need for any level of salvation become a moot point. The entire biblical narrative collapses and from their position, rightly so.
With fundamental literalism, there is no middle ground, no area of compromise. Not all christians are this way obviously but at the moment those christians appear a minority. But I do think the pressure is on with the rise of people identifying pertaining to religion as a none. There is a growing panic about this condition and as is grows, watch for the "War On" claims to multiply.
It's pretty obvious that a majority of the world's population feels compelled to believe in some sort of supernatural narrative so rather than cherry picking just the parts you like from an existing narrative that doesn't fully reflect your values why not just come up with your own belief system that really does reflect your values? It's how all these religions got started in the first place anyway.
People are at this point in their evolution hardwired for some form of belief, vast majority do and will continue and I see nothing that will change that. They may abandon dogma and doctrine but even in some form they come up with themselves, belief in some manner of higher power will continue.
