I don’t think you’re going to be able to keep this out of GD, honestly. I’ll try to give you a brief summary of events that may be why Sharon was labeled a “war criminal”, but please remember, this is probably pretty inaccurate. I’m doing it from memory and have my own biases, of course, like most people.
A number of Palestinian refugees moved into Lebanon after they left Israel, and set up refugee camps there. The camps were also headquarters for Palestinian terrorist groups, like the PLO, who would use them as bases from which they launched raids into Israel. The Israelis, as you might imagine, didn’t like this, so they invaded southern Lebanon.
First the Palestinians, then the Israelis exacerbated an already tense political situation. Lebanon is split almost evenly between Muslims and Christians, and they don’t much like each other, due partly to the Ottomans favoring the Muslims during their rule over Lebanon, and then the French favoring the Christians. The Lebanese worked out a compromise government, involving quotas of Muslims and Christians, mandating that the President be Christian, the Vice President be Muslim, etc. This worked about as well as you might expect, and Lebanese politics became very fragmented, with individual parties having their own militias, and violence becoming an accepted political tool.
Anyway, what happened was, a Muslim group assassinated the (Christian) President during a military parade. The assassins, suspected assassins, and people who were or could have been involved in the assassination fled into the Palestinian refugee camps, which were in the Israeli occupied zone. At this point, the ex-President’s militia said to the Israeli Army, “Look, these people killed the president and we know they’re in the camps. Let us go in and get them.” The Israelis, for a combination of reasons (They had good relationships with the Christian millitias, they wanted to embarrass the Palestinians, they didn’t like the idea of assassins running around free, etc.) said yes. The militia then went into the camps and started massacring people.
This incident led to an outcry among the Israeli public, and the Israeli government began an investigation. The panel pinned blame on and officially criticized a number of Israeli generals and government officials, including Sharon, who was Minister of Defense, saying basically, “How idiotic do you people have to be to let vengeful people with weaponry, who don’t like Muslims into a mainly Muslim refugee camp where they suspect the people who killed their leader are hiding?”