In Holland this was a valid reason to request two passports, like if you frequently travel to both Israel and Egypt. They are mutually exclusive.
And it's easy to find out which countries a person has been to, because passenger lists on planes are pretty much public knowledge so it would be an easy lie to detect.
Not a problem for this guy
No idea about now.
Some countries (Syria etc) will not only not let you in with an Israeli stamp, but also any sign of visiting Israel - money, snacks, etc.
The main problem nowadays though is the US - they won't let you in without a Visa if you've been to places like Iraq or Libya since 2011. A colleague went to Syria a couple of months ago, I asked "are you happy you'll never be eligible for an esta again". It's fine for now as work will pay for a US visa, but in 20 years time when he's retired?
That's a fair bit of hypocrisy considering how many of their own soldiers they sent to Iraq.
I don't think I'll ever visit the US again though. So I wouldn't care about an ESTA. It's turning into a conservative religious place. I avoid those, like all of the middle east.
I'm trying to get an X in my passport so the US will simply deny me entrance. That way I can just say no to work if they want to send me there for a meeting or a tradeshow. I'm kinda genderqueer anyway (though not full non-binary) so that would be a good match. And if the US ever gets a sane government again I'm sure they will reverse this stuff right back.
Unfortunately my own government is also turning radical right conservative so they are making this harder :(
Reverse it? This was Obama's idea.