Some people feel there is no way for such a "feeling" to form spontaneously out of the cold, dead matter. Since some matter doesn't experience this feeling, how does it spontaneously form, out of no-feeling, at some threshold configuration? What is this threshold exactly? These people think it must special, since we can imagine (in principle) a clump of matter interacting physically in time to simulate the external appearance of a human mind, yet remain no-feeling on the inside.
Other people don't seem to grasp what the problem the first people are posing might possibly be. The "feeling" is simply a property of the universe which arises in some physical configurations. Computers can have subjective experience and even today's computers might have it in some form. There is no discrete, magical step required.
I find myself continually switching teams on this matter. The second position might be more believable after we find some laws governing the relationship between physical configurations and the nature of the resulting experience. But since subjective experience is necessarily... subjective, it seems very hard (impossible?) to test.
Personally, I don't see a basis to believe there's something more to it. I'd look at the cluster of atoms in your brain and say this is anger. This is the computational process that is anger in your brain. I don't see a meaningful difference between this and doing the same to a computer - I could point at a cluster of atoms and EM fields in the CPU and say, "this is factorization of numbers; this is how the cryptographic routine this CPU executes manifests". Why would there be anything else here?