Some have suggested that rejecting the doctrine of double effect  would have "consequence of putting us hopelessly in the power of bad men." What reason is there to believe this? Do you find this claim plausible?

The doctrine of double effect is a claim about moral significance of the distinction between intended harm and bringing about harm as a foreseen but unintended side effect of ones action. The core claim of double effect claim is currently understood to be sometimes permissible to bring about as a foreseen but unintended side-effect of one's action some harm would have been more impermissible to aim at as a means or as an end ,all else being equal. With this it is evident that by rejecting the doctrine of double effects there would be consequences of putting up with bad omen. I find this claim reasonable.