Meh, in a pinch I'd bet they'd stretch. I'd be far more weary of trying to shove a 1-1/4" into a 23.

But yeah, I agree with your basic premises. If absolutely nothing else, one should have their own tube. If I were on my own long ride, I'd be hesitant to give up my only tube to someone else who wasn't prepared, because my theoretical protocol (even though all my bikes are equipped with spares and tools, I've thankfully never had to use them) includes heading back once tubes have been swapped. I really need to toss some patch kits into my bags, I think.