I don't mean this to sound pernickety: steelmanning from what I've seen normally is a lot more active than just treating the opponent charitably. Often it involves a lot of work trying to rework the other people's ideas from the ground up. It goes beyond charity in a way that's probably too labour intensive to apply except selectively.
It's interesting to compare with other flavours of charitability:
Take the definition of steelmanning from lesswrong:
> Steelmanning is the act of taking a view, or opinion, or argument and constructing the strongest possible version of it. It is the opposite of strawmanning.
vs. Dennett's recommendation in arguments ( https://en.wikipedia.org/wiki/Rogerian_argument#Dennett's_ve... )
> "You should attempt to re-express your target's position so clearly, vividly, and fairly that your target says, 'Thanks, I wish I'd thought of putting it that way.'"
These mandates aren't exactly the same ( It might be that your strongest way of phrasing an argument wouldn't be accepted by the original argument-giver, for instance), though both could be seen as kinds of charitable engagement.