What evidence are you talking about? Sharon refused to allow the U.N., the press, or even various aid groups into the area. True, the total death count probably wasn't enough to qualify it as a massacre, but destroying the entire civilian infrastructure including water, electric, and other utility lines certainly goes beyond what one would consider a defensive action-it was more an act of collective vengeance against the entire civilian population, not just against the terrorists.
Second, less than 6 square city blocks were razed in rooting out the terrorist and thier bomb making factories... satalite photos, from a U.S. satilite are available on the IDF web-site (sorry for not having the link handy). The Area razed comprised less than 10% of the camp. If anything, the Israelis were guilty of being too humane in dealing with the terrorists in Jenin and unecessarily risking their soldiers lives.
Israel rightfully denied the U.N. fact finding team in when they learned it was Predispossed to reach a "massacre" outcome without properly analysing the evidence... The head of the U.N. team had previously equated the symbol of the Star of David on the Israeli flag with the Nazi Swastika. Israel's request was simple, put military experts on the team who had experience with counter-terrorism measure, and the U.N. balked.