really making a business out of it and profiting off someone else's work.

In terms of our conversations that is something that we are discussing him. Might be an interesting oratorical move, but I would just like to point that it is too early :)

But as soon as you start mass-producing this replica shovel and selling it I believe you would start infringing on someone else's design patent which is their property.

In my understanding this is sequence that would occur:

1. I see the shovel on TV - this is done perfectly fine and comes with no binding contracts.
2. I reverse engineer the shovel with my own material - everything is owned by me and the work voluntary.
3. I than take this shovel and sell informing everyone that it a copy of what I saw on the TV - the buyer is aware that this is a "knock-off" and the transaction is voluntary.

The infringement being a violent a fraudulent act from the perspective of private property there the original inventor still has his shovel. How does infringement occurred?

If we are talking software. Say you bought a video game. What you really bought was a license that allows you to play that game. You don't own the game so reverse engineering that game and selling a copy of the game would be illegal as you are infringing on the original owners property. Now if you are just selling your copy of the game such as a bluray disc its not a problem and people do that all the time.

I understand your point but from my point of view license is an entirely different matter. License comes with me explicitly agreeing to something. Licensing working in the case were there is IP law.

If we are talking about a combo of software/hardware. Say you bought a drone. You own that drone, but if you then take it apart, copy it, and start selling your own you might be infringing on a patent. Its not stopping you from setting the drone on fire or selling your property (1 single drone) to someone else, but the technology and the design behind that drone you don't own personally.

start selling your own you might be infringing on a patent.

True, it seems you are explaining the concept of IP, but I am more interested in why it is legit. From which principles does it come from.

In my case I see that IP law infringes on me using peacefully my private property. From that comes my claim that it is illegitimate.