The author fails to consider that an action (demolishing) may be morally permissible even if an alternative course of action (using the base for other purposes) is to everyone’s advantage. (A) shows that the author’s premise doesn’t establish demolishing the building was immoral.

The author doesn’t assume that actual consequences are irrelevant. After all, one actual consequence of demolishing is that the base can’t be used for the purposes described. This is something the author takes into account and uses in the argument.

The author’s argument concerns only the demolishing of the former naval base. The author concludes that this action was inefficient. That doesn’t commit the author to an assumption that the government never acts in the most efficient way.

The author does not assume that if an action is efficient, then it must be moral. The conclusion is that the government’s action was inefficient and also immoral. This doesn’t commit the author to a belief about a conditional relationship between efficiency and morality.

The author does not treat demolishing the base and using it for other purposes as the only options. For example, maybe the government could have left the base up and just abandoned it completely. The author doesn’t assume this wasn’t possible.