Their justification, at least in the United States is Article 1, section 8, clause 8 of the Constitution: “To promote the progress of science and useful arts,

Their justification, at least in the United States is Article 1, section 8, clause 8 of the Constitution: “To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries.” You can argue the meaning of "limited times" and "discoveries" and the interpretation of all that, but the justification is that by providing a limited monopoly, the inventor gets a period to make money uncontested, after which the invention is available to the community. The alternative, a "trade secret", means that the invention may die with the death of the inventor and be lost to the community.