Somehow even less of an advocate for peace than Ronnie Reagan. HP
There are many things to criticize Begin for but I mean, he signed one of the most important peace agreements in the Middle East since WW2. He stopped what was a state of constant war- either active fighting or preperations for a future war- between two of the most important countries in the region. This is an advocacy for peace, I'd say.
Stopped a state of constant war? The man straight up invaded Lebanon, destroyed the Palestinian societies there, and then rejected Reagan's peace proposal, despite the international outcry of the Sabra and Shatila massacre which Begin's defense minister Sharon conveniently called a "mop up."
Now, granted, the Reagan proposal wasn't great - it, too, was a rejection of the two-state solution and denied the Palestinians a state - represented a federation between Jordan (which Israel and the U.S. have long maintained is the "real" Palestinian state) and parts occupied by Israel which had originally been proposed by King Hussein but was rejected by Meir. Reagan also called for a freeze on the settlements in the occupied territories, which have expanded even to this day (although, by that point, more than half the land had been seized anyway). But Begin's government was an expansionist one, so he resoundingly rejected the proposal which was still largely pro-Israeli by most international standards.
So, as for the Camp David Accords, which I presume is what you're referring to, it's pretty obvious here that Israel under his administration did not even remotely live up to the ideals of peace, and the accords further divided up the West Bank (without the consent of the Palestinians). They may have neutralized Egypt, but that only allowed further Israeli terrorism agains the PLO, expanding settlements, all in major violation of international law.