(b) Yes, this is the better argument. Failure to take steps to avoid foreseeable harm may be justified in some circumstances. For example, the steps needed to avoid harm may involve a risk of other, possibly greater, harm. In other cases, there may be competing responsibilities, each of which involves a risk of harm; or the social utility of an activity may justify taking the risk of foreseeable harm.
In the case-study, it might be argued that to restrict the use of the airport would cause great inconvenience and even economic harm. Such arguments may not be sufficient to justify inaction. But it might also be argued that restricting flight paths and operating times would cause congestion of air traffic and increase the likelihood of collisions or other accidents. It may arguably be reasonable to prefer to avoid these risks, even if it means accepting other possible harm.