Walt normally would have been glad to go with them but they were forgetting their mission and he decided that now was yet another time to be serious. he ran in front of them and blocked their way

"we have a mission to complete which was to not get involved with the battle and do some recon, there two reason why we shouldn't fight, one this is metropolis and superman and the other godlike heroes protect this city, two we would be potential casualties and would get in the way of the heroes" he told them.