The claim that the Israel Lobby yields outsized influence is hard to assess. Without question various individuals and groups advocate strenuously for U.S. support of Israel. The U.S. electorate is broadly supportive of Israel, however, so the apparent influence of the Lobby is perhaps a reflection of this general perspective, rather than an independent factor.
The claim that support of Israel harms the U.S. is the more fundamental issue, however.
In my view the authors are correct on this claim, and I would go even further. It was a mistake for the U.S. to help create Israel in 1948, and it is a mistake for the U.S. to provide financial or military support now. The creation of Israel endorsed the notion of a sectarian state, and it generated the virtually unresolvable problem of displaced Palestinians. Ongoing U.S. support of Israel produces bitter resentment in the Middle East and likely generates far more terrorism than it prevents. Against these negatives, any benefit to the U.S. from support of Israel is hard to discern.
Israel now exists, so the question of whether it should have been created is moot. But continuing U.S. support is not a given. It is time for open discussion of this issue. The Mearsheimer and Walt paper is an excellent start.