Good point. When someone says "Bless you" to me (whether it's for a sneeze or to thank me for something) or "Merry Christmas" or the like, I don't say, "I'm an atheist you jerk!!" I just accept that someone is being nice to me, and appreciate the sentiment (if not the form).
That's become my attitude.
I use gesundheit.
I have never said "bless you" or anything like it. Not even when I was religious because it seemed like a stupid thing to need to be blessed for. I usually ignore it but I will say "thank you" if someone says it to me just because I don't like having to explain my somewhat rude behavior.
"It was good of you to sneeze without farting."
More seriously, when I say anything at all it's usually "Gesundheit!" This means "health" in German. Which is a strange thing to say, if you stop to consider it's just a noun, not a complete sentence.
I guess it's a shorthand wish for someone with the sniffles to be healthy again. I'd rather extend tidings of health than spiritual blessings, since health is actually tangible.
I'm pretty sure that sneeze responses were invented just to get over the awkward moment after the sneeze. I wish they had invented a phrase to say after someone farted...maybe, 'out with the old, eh'
I might have to start saying that.
"Out with the old, in with the PHEW!" (while holding one's nose)
Or substitute "PEE-YOO" for "PHEW."
After embarassingly loud burps and farts, I like to say, "better out than in, right?" We're all human--just a gooey, gassy animal.
I dropped that traditional rhetoric when I grew up. Bothers me more when "doG Bless You" is said to me. For any reason other than sneezing, I know most are climatized to the traditional terminology. Any other reason would be judging me.