A line item veto is a far, far worse prospect. As much good as you think it could do with a president that had good intentions, imagine the harm that it could do in the hands of someone like Trump? Passing bills that are remotely bipartisan require a certain amount of compromise; if any of the people involved know that the things they wanted in a bill get stripped out by a hostile president, hen there's absolutely no reason to compromise at all. That's a very bad thing, since it results in complete gov't shutdown and permanent gridlock even if you have a single party controlling every branch of the gov't.