To put steelmanning in software terms: if we’re arguing about what algorithm to use to solve a certain problem, I can assume you’ll work out all the bugs in your implementation (in your example: e.g. getting capacity/speed numbers slightly wrong for some modes of transportation), and focus on the core algorithm instead (e.g. that transitional period is something that definitely needs to be addressed)
While this lady was courageous enough to be willing to put her bigotry out in the open, for every person like this, there's 10 more locals with similar sentiments who are self-aware enough to not say the quiet part out loud. This is a weak point within NIMBY arguments -- that often they don't want "those people" around, whether that be a matter of race or class -- but it's not merely a bug you can iron out, because it's actually a core motivator for their political position. It has to be, or at least should be addressed.
"Act as if your opponent isn't racist or classist" means partially detaching yourself from the reality of the situation, if the current situation is that they are, in fact, racist or classist.
In other words, steelmanning risks misrepresenting your opponent's
actual position -- exactly the same flaw as strawmanning, but in the opposite direction.
There's two things at play here. One is your political opinions vs theirs, the other is your arguments for how you should handle a specific concrete situation. Crucially, the former doesn't (edit: necessarily) change the merits of the latter.
Would you accept the thrust of their argument if it came from a different (non-racist/classist) speaker? Then their racism is just a bug you can dismiss. Focusing on it is actually a straw man, because that's not germane to the argument they're actually making!
Does the argument hinge, at its core, on unspoken racist assumptions? Then it's a fundamental part of the argument and you need to tackle it.
