The argument I provided in the message starting this subthread that you answered, was to repeal the Jones Act COMBINED with enacting other subsidies and investment to revitalize US domestic shipbuilding and the maritime sector. Merely repealing the Jones Act without any of the other measures would indeed lead to a quick collapse of what little is left of the US civilian maritime sector.

(Nuclear option: US Navy ensures Freedom of the Seas only for US flagged vessels. Your Liberia-flagged ship gets attacked by pirates, or even some state actor? Ask the Liberian navy to come to your help. And no, this isn't really a serious suggestion that would be in the US interest.)