"We believe in talking birds (African Grey Parrot)."
Birds don't talk; they mimic. While Alex, probably the most famous African Grey parrot, counts and can distinguish colors I wouldn't call it speech.
"Why is a talking snake such a stretch?"
Lack of vocal cords, incorrect musculature and other anatomical hurdles make it exceedingly unlikely that snakes will be speaking to anyone anytime soon without the help of hallucinogens.
"We have evidence of an animal that speaks today, yet no one can prove that snakes have never spoken."
Well, my dog "speaks" when I tell her to. She has a very limited vocabulary consisting of "woof" though so it's a rather dull conversation. Other than that, I know of know animals that "speak."
We know snakes have never spoken because, aside from the previously mentioned anatomical impossibility of it, I doubt their brain would be capable of it. Not only that, snakes have no ears and are virtually deaf so speech would be rather useless, no?
"It all seems so silly."
You said it.
"If atheist want to label faith as fantasy, perhaps they should pick better examples."
No, I think belief in talking snakes is a pretty good example. Of course there's always Balaam's Ass which also spoke...