This is the correct assessment. It is on those making claims that require the burden of proof.

The claim is that "sacrificing liberty is providing us more safety" __not__ "our sacrifice of liberty has been ineffective at providing more safety." The latter statement comes from the lack of proof from those that carry the requisite burden. The former claims were made when liberty was initially eroded. Now that we have had time and calmed down people are asking "was it worth it?" and no one has provided a compelling "yes, here's (with evidence) why".