The problem was, no one saw tapes of Hitler's atrocities and hardly anyone knew there was such a thing as a concentration camp. To most people, the "holocaust" part of WW2 came as a surprise at the end of the bloody war that pitted Nazi soldiers against soldiers from other countries.
For exactly this reason, I think the tape should be shown. We do need to know what the Muslims are doing, especially when they're doing it to an American citizen. Also, what about those of us who travel? Shouldn't we be making informed decisions about touring Muslim countries? If American tourism falls off, those Muslim governments may well feel the financial pinch and rush to do round up terrorists in their midst.
I forced myself to look at that Chechan beheading, believing that I owe myself the whole truth. If the Pearl beheading tape is show, I suggest that they edit out all the anti-American propoganda and leave in only the "I am a Jew" part and the beheading itself.