Argueing against creationism is equal to trying to break down a brick wall by smashing your head into it repeatedly. Not going to work unless maybe you have a few million heads and alot of time.
Creationism is a theory like "the world was shat out by a yellow-bellied sapsucker last sunday" is a theory, and it has just as much empirical weight behind it.
It's all about practicality. Physics helps us build computers, chemistry helps us make fertilizer, and evolution helps us find medical cures. What is the use of creationism?
Yes, both religious people and reality-based people have a point where they'll be forced to say "I don't know" if you keep questioning regressively.
The strength of science is that it thrives on "I don't know" - every "I don't know" is a pathway opened to new advancement and new understanding. For a religious person "I don't know" is filled by the gap of "god did it". This is what makes religion a useless means of interpreting the world - it's closed, masturbatory, and dogmatic.
Basically, you're claiming that if you can't know everything, you can't know anything. I call enormous motherfucking bullshit on that. Sure, we don't know everything about how the universe works. There are vast, unimaginable mysteries out there for us to discover. That doesn't mean we don't know enough to build a fucking space ship. Building a space ship is how we get closer to finding and understanding those mysteries.
The same way, science may not be able to answer questions of abiogenesis or universal origins completely, but we have enough solid, empirical evidence RIGHT NOW to say that the creation story, as it exists in the bible, is absolutely and completely wrong on all counts. Hell, we've had that for over a century; it just keeps getting stronger.
Don't be mistaken and be under the impression that both science and religion are things people retreat to to avoid having to say "I don't know". On the contrary; science is for people with the wisdom to say "I don't know", and the courage to look for answers.