It generally seems at least as reasonable as any other form of IP protection. After all, the underlying principle is that the creators of an 'invention' deserve some kind of protection from others who would profit from their work without requiring the same level of investment – with idea that it's better for society in the long term to avoid a 'race to the bottom'. I'm not sure that's particularly different whether we're talking about creative work, physical inventions, manufacturing processes, computer software, or design languages.

It does seem that the rules governing them need to be revised. Many patented ideas are utterly trivial, or have no practical implementation, or are just unused. The terms are clearly too long as well. But the underlying idea doesn't seem terrible.

No. The entirety of intellectual property is a pure construct of human convention. At one end of legitimacy is the right of proper attribution, and at the other end is the right to be a patent troll. The US does not do a great job in setting the balance points.

Copyrights should not apply to any functional work. Trademarks should not be used to stifle discussion, review and criticism. Patents should require expert testimony on originality and also a working example.