Liberals are frequently unaware of their blind spots (but if you take care, they can be corrected). And then there's a swath of conservatives that don't think they're racist. If you should suggest it, it's too easy for them to dig themselves deeper into a hole.
All too frequently, I'll wish I stuck to non-political / comfortable topics – and remembered that political-correctness is there to protect me as an individual, so I can live in my bubble and get on with the day, even though PC-culture might be bad policy for society.