The word "alone" here is not correct. Claiming that software on a computer can produce feelings is not the same as claiming that software on a computer can produce feeling without having to interact with anything else. The latter claim is obviously absurd; organic life forms like us don't produce feelings without interacting with anything else, so why should we expect software on a computer to do so? But ruling out the latter claim still leaves open the possibility that software on a computer could produce feelings if it were interacting with the rest of the world in appropriate ways.

> I do not think consciousness necessarily can only be produced by organic life, but I do think it has to emerge from physical structures.

Rocks in a certain pattern are physical structures. So this doesn't rule out rocks in a certain pattern producing feelings.

> As of today we have no idea what properties such physical structures must have.

I don't think we're that badly off. We expect embodied brains of sufficient size and complexity to produce feelings, but we don't expect three pounds of jello to produce feelings. So clearly we have some knowledge of the properties that physical structures must have to produce feelings. They must have some level of complexity and heterogeneity; they must be able to store information in some way that is recoverable (three pounds of jello can "store information" in some sense, but there's no way to recover it in any useful sense); and they must be interacting with the rest of the world in appropriate ways. There's no reason why we couldn't eventually build computers with these properties.