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.

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.