http://www.countryreports.org/travel/Israel/entry.htm
“Those with extensive travel to Muslim countries or U.S. citizens whom Israeli authorities suspect of being of Arab, Middle Eastern, or Muslim origin may also face additional questioning by immigration and border authorities, particularly if they ask that Israeli stamps not be entered into their passport.”
An Israeli stamp in the passport is big trouble for those visiting Muslim countries. People reapply for their passports in order to avoid it.