That's a little extreme. And the example you yourself cite demonstrates just how incredibly inconvenient it can be to deal with a mistake made by the Israeli immigration agent if you only have one passport. They do, in fact, occasionally stamp passports even when you've asked them not to (if you're still feeling statistically minded, note that three of the seven posters in this thread have cited or alluded to personal experience with this practice). In my case, there was no confusion, no shift change, no long questioning process. I clearly asked for my passport not to be stamped when I stepped up to the counter, and about 15 seconds later, the agent stamped it and handed it back. Luckily, I had given her my 2-year passport anyway (my regular passport is the one I use for getting into places like Lebanon). So for me, no giant hassle ensued--but had I been on a single passport, there would have been one.