Steelmanning is not a courtesy or a service to my interlocutor. It is a service to me. It is my attempt to build the strongest case I can against my position, so I can shatter it or see it survive the challenge. The interlocutor might not agree, if I were to ask them, that my steelmanned argument is really stronger than theirs; that's no matter. I'm not doing it for them, I'm doing it for myself.

Steelmanning is always done for your own sake. It always says something new that the original owner of the argument didn't think of or at least didn't say. When put back into the discussion, it should be introduced explicitly as your words.

Remember, the steelmanned argument is your creation and is meant for you, you owe it to yourself to test your beliefs with it, but not necessarily in the context of this conversation. Not because concealing it is an easier way to victory, but rather because what's steelmanned for you might not be steelmanned or even interesting to your interlocutor. Their argument said A, and you may have found a way to strengthen it further to say B, but they might not want to claim B, to defend B, to agree that B is stronger than A. That said, if you do think the steelmanned argument would be useful to them, by all means introduce it, but explicitly as your own.

I agree, and this is sort of what I find problematic, I'll explain in a second. (Notice that all four "risks" I mentioned are risks to the Roman and not the progressive.)

Now, going to the example in the post, where the ancient Roman chooses to interpret a progressive argument for increasing welfare as "really" carrying between lines the ancient Roman rationale. He is not doing a charitable reading of his interlocutor's words - they would definitely not agree that this is what they meant to say. And he is not steelmanning anything either, because he hasn't strengthened an argument against his own position; rather, he fortified his existing beliefs by manufacturing another fake confirmation. If he were to modify the progressive's argument in some way that would make it harder for him to interpret it in the ancient-Roman sense, that would be steelmanning.

I think I was a little unclear here, sorry. Imagine that the Roman is already against increasing welfare, for whatever reason. He first reads the progressive article and thinks that the progressive's argument is dumb. He then remembers steelmanning and re-interprets the article as arguing that welfare reform would incur Anonna's favor. He finally realizes that the position isn't that bad when seen in this light, and begins to be a little less certain that increasing welfare would be a bad idea. This is sort of what I was imagining when I wrote the post. The belief that's being tested is not the entire ancient Roman worldview, it's whether or not welfare should be increased.

The thing is, when the Roman creates the new argument "increasing welfare would incur Anonna's favor", that's a completely new idea that he came up with himself, and as such it should be held skeptically. Imagine if Anonna in fact liked welfare when it was in the form of gold coins and hated it when it's in the form of a vague baseless digital currency, and the Roman had no idea, not being an Anonnan priest. However, he might mistakenly think that the fact that the idea "we should increase welfare for equality" is fairly popular and held by smart people is authority for the idea "increasing welfare would incur Anonna's favor", but in fact these are pretty distinct ideas.

I feel like the steelmanning process usually outputs a new argument that you can look at and say "yeah, that kind of makes sense". But I was reading some of the "Tupac is alive" conspiracy theories the other day, and I thought they kind of make sense. For me, an argument kind of making sense is pretty bad evidence for its truth - good evidence would be if I read the argument, then the rebuttals, then the rebuttals to the rebuttals, then the rebuttals to the rebuttals to the rebuttals, and etc. until I finally found a point where I could say "okay, that really does makes sense". But I haven't had the time, or likely the ability, to do this with most arguments, so I usually form my beliefs off of vague intuitions around authority. What I guess I'm afraid of is that I'll conflate my original steelman with a superficially similar popular argument, and then these intuitions will get corrupted and I'll be confused.

Obviously the Roman thing is a pretty dumb cartoony example and it seems too obvious to fall for in real life, but I feel like this usually works on a much more subtle, implicit level, and in fact I think that's why I have a lot of trouble putting it into words. I find this topic really confusing to talk about, so hopefully I didn't say anything too dumb. I think I mainly agree with your post, though, and what everyone else is saying. Again, I think steelmanning is 90% a good thing.