"Do atheists and theists agree that it is impossible to decide whether or not God exists?"
We can't even agree that we don't agree.. I was often told that subconsciously i am actually a believer and at some point in my life i will turn "back" to Jesus or Allah or the easter bunny's evil twin.. or something among those lines.
An atheist doesn't need to prove it, for us its enough to not believe it.
For a theist to prove that god exists he would have to KNOW that a god exists, but they are called believers because they don't know it, they just believe it. Yet they don't say "i don't know if god exists but i believe he does" most of them say "i know god exists, my proof is that the bible says it" or "who else did -input alleged miracle- if not god?!" etc and to back it up some often pull out the *undeniable* "and you will burn in hell/jahannam/Detroit's sewers for eternity if you don't believe it"- argument.
I can't agree with somebody who claims he knows something that he just believes.. At least not on related topics, so no, we apparently can't agree that its impossible to decide. They already decided it almost irreversibly so their brain shuts off and will ignore even obvious and undeniable proof that their teaching is disproven by itself, no need for us to add anything.
However to actually be able to be disproved, you would have to allow some input to be able to process it, and since the brain shuts off at that point it won't allow any input. They even deny facts straight from the Qur'an or Bible or the Mianus phone book (if thats where they got their belief from), because they cling to their own (often very flexible) version and not the actual teachings.
In rare cases you manage to smuggle in a tiny ray of light into the darkness but sadly, mostly it isn't enough to illuminate anything.
Also you said:
"The only excuse for not accepting this consensus is lack of education - and that is not an excuse."
Did lack or education or rationality ever stop a "true believer" or an idiot from sticking to any claim/statement no matter how absurd? Not that i knew.
ps. in THIS case i am not refering to believers as idiots althogh i am tempted.. knowing they prefere their saddistic omnipotent imaginary friend over logic reason and humanity.