Any organism that responds in any way to mitigate damage to itself must be responding to a pain of some kind. Having said that, I'm also sure humans experience pain differently than lower forms of life do.
False assertion. Reflexive and automatic behavior has no need for pain- pain is only present where there is cognition and the ability to learn and adapt in a dynamic way. If it looks like a duck, and quacks like a duck... Pain serves exactly the same purpose in all life forms capable of basic cognition- it guides the evolution of the neural networks with negative feedback. The qualia is of an inherently identical nature. It may exist in varying quantities and degrees- depending on capacity for cognition- but the nature is the same. If you're skeptical about that, you're making the same philosophical blunder as a solipsist.
When I pull my finger away from something hot, that's automatic behavior, but being burned still hurts like hell. I really can't say how a slug feels when it gets burned and neither can you or anybody else. All we can do is observe the physical reaction. I have no doubt that the slug hurts when it gets burned, I just don't care very much whether it in pain or not.
I didn't say it wasn't sometimes accompanied by pain (in your example, reflexes and learning function side by side). An automatic reflex doesn't provide evidence for pain, though. Those we know don't feel conscious pain, like the brain dead, can also have reflexes and encapsulate foreign material. Likewise, plants which are equally incapable of feeling pain can act quickly and reflexively through a cascade of simple chemical reactions (such as fly traps closing). Of course that's fair- a garden pest is a garden pest. Whether they were tiny gnomes with complex societies, art, music, etc. or mindless blobs incapable of sensory perception at all, they'd need to be eliminated to protect our food supply. It is certainly more comforting to imagine that they are closer to the latter than the former- though that doesn't make it true. If we strive to be critical thinkers, we should be extra careful with our assumptions when we have such a motivation to lie to comfort ourselves. We'll just have to disagree on that point. I think it's quite easy to say, and anything else resembles to me overly severe philosophical skepticism.
