The reason why Saudi Arabia uses crucifixion is because it is prescribed as a punishment in the Quran, and the constitution and legal system of Saudi Arabia is the Quran and sunnah. No other reason.
On what basis should citizens other than those that reside in that nation state be involved in the outrage? Surely a nation state can do what it likes, as long as the practice does not affect any other nation state, and vice versa...unless you want to enforce your own world-view onto someone else (this works vice versa, of course, too). If the citizens of that nation state don't like a practice, they, not anyone else, should do something about it, no matter how hard it is for them. By extension, another country's practices are their own, and should not be meddled with by anyone else...unless politicians, led by big business, have somehow decided otherwise. Oh.
When a country has as much oil as Saudi Arabia and are also allies with the west, they can get away with just about anything.
It's wrong but at the end of ye day he chose to break the law. He had his own free will so stop crying. Just obey the laws of that country, if it's extreme then move elsewhere.