Whether or not sending more troops is a good idea is certainly debatable, but more troops dying isn't one of the cons. Having more troops there isn't going to increase the casualty rate(it may lower it as it'll be harder for the insurgents to plant IEDs with more resources to look for them). The main issue is that sending more troops isn't sustainable for more than 3-6 months, so unless whatever it is that they think needs fixing can be accomplished in that timeframe, it's probably not beneficial. The problem is that Iraq is a sovereign nation now, so we can't necessarily go after everyone that we'd like to. The government is predominantly Shia, so we can't just go wipe out the Shia militias without their support(which we won't get). Unless we have the thumbs up from the government, it's much more difficult to go pacify problem areas.