you can store your private keys printed inside a deposit box if you don't trust computers (which you shouldn't). Nobody guarantees bitcoin, but insurance companies will always exist.
Even with cash, you trust that the banks won't blacklist your serial numbers. With gold you trust that the world will not invent a new gold making method that will make it worthless (as happened with aluminum). A basic level of faith is required by any system, so that point is not valid.
The blockchain is a virtualized state - yes it executes on computers but the whole point is distributed consensus - you don't have to trust the computers, you trust the open source code being executed by the network.
I don't think you're using the word 'trust' correctly. Trust is a belief that a particular outcome will occur despite having no guarantees that it will occur. What does it mean to trust the law? I have no idea.
I think you are quibbling over the word "trust". How about you believe, based on your understanding of the system and the monetary cost of attacking it, that the virtualized computer will execute the way you expect it to execute?
The same way you'd "trust" that a safe deposit box will not be breached. It's certainly not impossible, but it's unlikely based on your understanding of how it works.