I see so much in your reply that suggests we agree even more than you acknowledge!
I agree that “being immersed in depravity is not something which in itself has any inherent tendency to destroy a person’s sinful propensities.” I also agree that “Until the evil passes a threshold of inconvenience in its results, the SSG would think being immersed in depravity was amenable.” The prodigal son’s depravity passed that threshold of inconvenience through circumstances unique to his case. Perhaps Paul saw that immersion in depravity would indeed cause the SSG to pass that threshold of inconvenience through circumstances unique to his case, too, even if it does not inherently or necessarily do that in all other cases. I mean if we are ready to say that Paul had the power to place an effective curse on someone, is it not as likely, or even more likely, that Paul had the power of perception sufficient to judge that an immersion in depravity would cause the SSG to pass the threshold of inconvenience?
But, despite that, I like your suggestion that there was a curse involved. I do have a question about a conclusion you drew, though. You said, “The phrase is much more likely to be a polite way of talking about being cursed with a painful and likely fatal result of his sins,” followed by “Then being cut off from the church would be meaningful to the SSG.” How exactly does being cursed with a painful and likely fatal result of his sins make being cut off from the church more meaningful to the SSG any more than would immersion in depravity, which itself could cause pain and death, despite superficial and temporary pleasure?