It is certainly used as an argument as to why atheists need not defend their position.But the burden of proof is not an argument at all anyway. Atheists do not use the 'burden of proof' argument, because it is not an argument.
It is not a "simple fact" that the burden of proof hasn't been met. I would say it is more like an opinion or a belief. Why? Because who decides this? After all, the theist likely would claim that he has met the burden.The simple fact is that the burden of proof for theism has not been met, and that disbelief does not bear a burden of proof.
Most people have replied that the individual that the theist is trying to convince decides. This makes the claim inherently subjective; and means that it could end up being arbitrary.
"If the burden of proof for evolution had been met, then there would be no Creationists."What I feel strongly about is the preposterous notion that the 'burden of proof' is an argument ever employed by atheists - it isn't an argument, it is just a convention that the person making the claim bears the burden of proof. If the burden of proof for theism had been met, there would be no atheists.
Do you see why that doesn't work?